LMH6611MKX [TI]

Single Supply 345 MHz Rail-to-Rail Output Amplifiers; 单电源345 MHz轨到轨输出放大器
LMH6611MKX
型号: LMH6611MKX
厂家: TEXAS INSTRUMENTS    TEXAS INSTRUMENTS
描述:

Single Supply 345 MHz Rail-to-Rail Output Amplifiers
单电源345 MHz轨到轨输出放大器

消费电路 商用集成电路 音频放大器 视频放大器 光电二极管
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LMH6611,LMH6612  
LMH6611/LMH6612 Single Supply 345 MHz Rail-to-Rail Output Amplifiers  
Literature Number: SNOSB00H  
January 26, 2010  
LMH6611/LMH6612  
Single Supply 345 MHz Rail-to-Rail Output Amplifiers  
General Description  
Features  
The LMH6611 (single, with shutdown) and LMH6612 (dual)  
are 345 MHz rail-to-rail output amplifiers consuming just 3.2  
mA of quiescent current per channel and designed to deliver  
high performance in power conscious single supply systems.  
The LMH6611 and LMH6612 have precision trimmed input  
offset voltages with low noise and low distortion performance  
as required for high accuracy video, test and measurement,  
and communication applications. The LMH6611 and  
LMH6612 are members of the PowerWise family and have an  
exceptional power-to-performance ratio.  
VS = 5V, RL = 1 k, TA = 25°C and AV = +1, unless otherwise  
specified.  
Operating voltage range  
Supply current per channel  
Small signal bandwidth  
Open loop gain  
Input offset voltage (limit at 25°C)  
Slew rate  
2.7V to 11V  
3.2 mA  
345 MHz  
103 dB  
±0.750 mV  
460 V/µs  
45 MHz  
0.1 dB bandwidth  
Settling time to 0.1%  
Settling time to 0.01%  
SFDR (f = 100 kHz, AV = 2, VOUT = 2 VPP  
Low voltage noise  
Output current  
CMVR  
67 ns  
100 ns  
With a trimmed input offset voltage of 0.022 mV and a high  
open loop gain of 103 dB the LMH6611 and LMH6612 meet  
the requirements of DC sensitive high speed applications  
such as low pass filtering in baseband I and Q radio channels.  
These specifications combined with a 0.01% settling time of  
)
102 dBc  
10 nV/Hz  
±100 mA  
−0.2V to 3.8V  
100 ns, a low noise of 10 nV/  
and better than 102 dBc  
SFDR at 100 kHz make these amplifiers particularly suited to  
driving 10, 12 and 14-bit high speed ADCs. The 45 MHz 0.1  
dB bandwidth (AV = 2) driving 2 VPP into 150Ω allows the am-  
plifiers to be used as output drivers in 1080i and 720p HDTV  
applications.  
Rail-to-Rail output  
−40°C to +125°C temperature range  
Applications  
ADC driver  
The input common mode range extends from 200 mV below  
the negative supply rail up to 1.2V from the positive rail. On a  
single 5V supply with a ground terminated 150Ω load the out-  
put swings to within 49 mV of the ground, while a mid-rail  
terminated 1 kΩ load will swing to 77 mV of either rail.  
The amplifiers will operate on a 2.7V to 11V single supply or  
±1.35V to ±5.5V split supply. The LMH6611 single is available  
in 6-Pin TSOT23 and has an independent active low disable  
pin which reduces the supply current to 120 µA. The  
LMH6612 is available in 8-Pin SOIC. Both the LMH6611 and  
LMH6612 are available in −40°C to +125°C extended indus-  
trial temperature grade.  
DAC buffer  
Active filters  
High speed sensor amplifier  
Current sense amplifier  
1080i and 720p analog video amplifier  
STB, TV video amplifier  
Video switching and muxing  
Typical Application  
30033629  
WEBENCH® is a registered trademark of National Semiconductor Corporation.  
© 2010 National Semiconductor Corporation  
300336  
www.national.com  
Supply Voltage (VS = V+ – V)  
12V  
150°C max  
Absolute Maximum Ratings (Note 1)  
Junction Temperature (Note 3)  
If Military/Aerospace specified devices are required,  
please contact the National Semiconductor Sales Office/  
Distributors for availability and specifications.  
Operating Ratings (Note 1)  
Supply Voltage (VS = V+ – V)  
2.7V to 11V  
ESD Tolerance (Note 2)  
Ambient Temperature Range (Note 3)  
−40°C to +125°C  
Human Body Model  
Package Thermal Resistance (θJA  
6-Pin TSOT23  
8-Pin SOIC  
)
For input pins only  
For all other pins  
Machine Model  
2000V  
2000V  
200V  
231°C/W  
160°C/W  
Charge Device Model  
1000V  
+3V Electrical Characteristics  
Unless otherwise specified, all limits are guaranteed for TJ = +25°C, V+ = 3V, V= 0V, VS = V+ – V, DISABLE = 3V, VCM = VO  
=
V+/2, AV = +1, RF = 0Ω, when AV +1 then RF = 560Ω, RL = 1 kΩ. Boldface limits apply at temperature extremes. (Note 4)  
Symbol  
Parameter  
Condition  
Min  
Typ  
Max  
Units  
(Note 8) (Note 7) (Note 8)  
Frequency Domain Response  
SSBW  
GBW  
–3 dB Bandwidth Small Signal  
305  
115  
AV = 1, RL = 1 k, VOUT = 0.2 VPP  
MHz  
MHz  
AV = 2, −1, RL = 1 k, VOUT = 0.2 VPP  
Gain Bandwidth  
(LMH6611)  
115  
135  
AV = 10, RF = 2 k, RG = 221Ω, RL = 1 kΩ,  
VOUT = 0.2 VPP  
Gain Bandwidth  
(LMH6612)  
130  
AV = 10, RF = 2 k, RG = 221Ω, RL = 1 kΩ,  
VOUT = 0.2 VPP  
LSBW  
Peak  
−3 dB Bandwidth Large Signal  
90  
85  
1.0  
33  
65  
AV = 1, RL = 1 k, VOUT = 1.5 VPP  
AV = −1, RL = 150Ω, VOUT = 2 VPP  
AV = 1  
MHz  
dB  
Peaking  
0.1  
dBBW  
0.1 dB Bandwidth  
AV = 1, VOUT = 0.5 VPP, RL = 1 kΩ  
AV = 2, VOUT = 0.5 VPP, RL = 1 kΩ  
RF = RG = 560Ω  
MHz  
47  
AV = 2, VOUT = 1.5 VPP, RL = 150Ω,  
RF = RG = 510Ω  
DG  
DP  
Differential Gain  
AV = 2, 4.43 MHz, 0.6V < VOUT < 2V,  
RL = 150Ω to V+/2  
0.03  
0.06  
%
Differential Phase  
AV = 2, 4.43 MHz, 0.6V < VOUT < 2V,  
RL = 150Ω to V+/2  
deg  
Time Domain Response  
tr/tf  
Rise & Fall Time  
Slew Rate  
1.5V Step, AV = 1  
2V Step, AV = 1  
2V Step, AV = −1  
2V Step, AV = −1  
2.8  
330  
74  
ns  
SR  
V/μs  
ts_0.1  
ts_0.01  
0.1% Settling Time  
0.01% Settling Time  
ns  
116  
Noise and Distortion Performance  
SFDR  
Spurious Free Dynamic Range  
fC = 100 kHz, AV = −1, VOUT= 2 VPP  
fC = 1 MHz, AV = −1, VOUT = 2 VPP  
fC = 5 MHz, AV = −1, VOUT = 2 VPP  
f = 100 kHz  
109  
97  
dBc  
80  
en  
in  
Input Voltage Noise  
Input Current Noise  
10  
nV/  
pA/  
dB  
f = 100 kHz  
2
CT  
Crosstalk  
f = 5 MHz, VIN = 2 VPP  
71  
(LMH6612)  
www.national.com  
2
Symbol  
Parameter  
Condition  
Min  
Typ  
Max  
Units  
(Note 8) (Note 7) (Note 8)  
Input, DC Performance  
VOS  
Input Offset Voltage  
(LMH6611)  
VCM = 0.5V  
VCM = 0.5V  
0.022  
±0.600  
±1.0  
mV  
Input Offset Voltage  
(LMH6612)  
−0.015  
±0.750  
±1.3  
TCVOS  
IB  
Input Offset Voltage Average Drift (Note 5)  
0.1  
μV/°C  
μA  
Input Bias Current  
VCM = 0.5V  
−5.9  
−10.1  
−11.1  
IO  
Input Offset Current  
0.01  
±0.5  
±0.7  
μA  
CIN  
Input Capacitance  
Input Resistance  
2.5  
6
pF  
RIN  
MΩ  
CMVR  
CMRR  
AOL  
Input Voltage Range  
−0.2  
79  
1.8  
V
DC, CMRR 76 dB  
Common Mode Rejection Ratio VCM Stepped from −0.1V to 1.7V  
98  
101  
85  
dB  
Open Loop Gain  
89  
RL = 1 k, VOUT = 2.7V to 0.3V  
RL = 150Ω, VOUT = 2.5V to 0.5V  
dB  
78  
Output DC Characteristics  
RL = 1 kto V+/2  
RL = 150Ω to V+/2  
RL = 1 kto V+/2  
RL = 150Ω to V+/2  
RL = 150Ω to V−  
RL = 1 kto V+/2  
RL = 150Ω to V+/2  
RL = 1 kto V+/2  
RL = 150Ω to V+/2  
RL = 150Ω to V−  
VO  
Output Swing High (LMH6611)  
(Voltage from V+ Supply Rail)  
59  
133  
59  
72  
76  
169  
182  
Output Swing Low (LMH6611)  
(Voltage from VSupply Rail)  
74  
80  
133  
42  
171  
188  
52  
56  
mV  
Output Swing High (LMH6612)  
(Voltage from V+ Supply Rail)  
58  
68  
73  
131  
61  
157  
172  
Output Swing Low (LMH6612)  
(Voltage from VSupply Rail)  
71  
79  
139  
43  
168  
187  
51  
56  
IOUT  
RO  
Linear Output Current  
Output Resistance  
VOUT = V+/2 (Note 6)  
±70  
mA  
f = 1 MHz  
0.07  
Enable Pin Operation  
Enable High Voltage Threshold Enabled (Note 9)  
2.0  
V
µA  
V
Enable Pin High Current  
VDISABLE = 3V  
Disabled (Note 9)  
VDISABLE = 0V  
0.001  
Enable Low Voltage Threshold  
Enable Pin Low Current  
Turn-On Time  
1.0  
0.8  
18  
50  
µA  
ns  
ns  
ton  
toff  
Turn-Off Time  
3
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Symbol  
Parameter  
Condition  
Min  
Typ  
Max  
Units  
(Note 8) (Note 7) (Note 8)  
Power Supply Performance  
PSRR  
IS  
Power Supply Rejection Ratio  
DC, VCM = 0.5V, VS = 2.7V to 11V  
81  
96  
dB  
mA  
μA  
Supply Current (LMH6611)  
3.0  
3.4  
3.8  
RL = ∞  
Supply Current (LMH6612)  
(per channel)  
2.95  
101  
3.45  
3.9  
RL = ∞  
ISD  
Disable Shutdown Current  
(LMH6611)  
DISABLE = 0V  
132  
+5V Electrical Characteristics  
Unless otherwise specified, all limits are guaranteed for TJ = +25°C, V+ = 5V, V= 0V, VS = V+ – V, DISABLE = 5V, VCM = VO  
=
V+/2, AV = +1, RF = 0Ω, when AV +1 then RF = 560Ω, RL = 1 kΩ. Boldface limits apply at temperature extremes.  
Symbol  
Parameter  
Condition  
Min  
Typ  
Max  
Units  
(Note 8) (Note 7) (Note 8)  
Frequency Domain Response  
SSBW  
GBW  
–3 dB Bandwidth Small Signal  
345  
112  
AV = 1, RL = 1 k, VOUT = 0.2 VPP  
MHz  
MHz  
AV = 2, −1, RL = 1 k, VOUT = 0.2 VPP  
Gain Bandwidth  
(LMH6611)  
115  
135  
AV = 10, RF = 2 k, RG = 221Ω, RL = 1 kΩ,  
VOUT = 0.2 VPP  
Gain Bandwidth  
(LMH6612)  
130  
AV = 10, RF = 2 k, RG = 221Ω, RL = 1 kΩ,  
VOUT = 0.2 VPP  
LSBW  
Peak  
−3 dB Bandwidth Large Signal  
77  
85  
0.3  
45  
68  
AV = 1, RL = 1 k, VOUT = 2 VPP  
AV = 2, RL = 150Ω, VOUT = 2 VPP  
AV = 1  
MHz  
dB  
Peaking  
0.1  
dBBW  
0.1 dB Bandwidth  
AV = 1, VOUT = 0.5 VPP, RL = 1 kΩ  
AV = 2, VOUT = 0.5 VPP, RL = 1 kΩ  
RF = RG = 680Ω  
MHz  
45  
AV = 2, VOUT = 2 VPP, RL = 150Ω,  
RF = RG = 665Ω  
DG  
DP  
Differential Gain  
AV = 2, 4.43 MHz, 0.6V < VOUT < 2V,  
RL = 150Ω to V+/2  
0.05  
0.06  
%
Differential Phase  
AV = 2, 4.43 MHz, 0.6V < VOUT < 2V,  
RL = 150Ω to V+/2  
deg  
Time Domain Response  
tr/tf  
Rise & Fall Time  
Slew Rate  
2V Step, AV = 1  
2V Step, AV = 1  
2V Step, AV = −1  
2V Step, AV = −1  
3.6  
460  
67  
ns  
SR  
V/μs  
ts_0.1  
ts_0.01  
0.1% Settling Time  
0.01% Settling Time  
ns  
100  
Distortion and Noise Performance  
SFDR  
Spurious Free Dynamic Range fC = 100 kHz, AV = 2, VOUT = 2 VPP  
fC = 1 MHz, AV = 2, VOUT = 2 VPP  
102  
96  
dBc  
fC = 5 MHz, AV = 2, VO = 2 VPP  
82  
en  
in  
Input Voltage Noise  
Input Current Noise  
f = 100 kHz  
10  
nV/  
pA/  
dB  
f = 100 kHz  
2
CT  
Crosstalk  
f = 5 MHz, VIN = 2 VPP  
71  
(LMH6612)  
www.national.com  
4
Symbol  
Parameter  
Condition  
Min  
Typ  
Max  
Units  
(Note 8) (Note 7) (Note 8)  
Input, DC Performance  
VOS  
Input Offset Voltage  
(LMH6611)  
VCM = 0.5V  
VCM = 0.5V  
(Note 5)  
0.013  
0.022  
0.1  
±0.600  
±1.0  
mV  
µV/°C  
μA  
Input Offset Voltage  
(LMH6612)  
±0.750  
±1.3  
TCVOS  
Input Offset Voltage Average  
Drift  
IB  
Input Bias Current  
VCM = 0.5V  
−6.3  
0.01  
−10.1  
−11.1  
IO  
Input Offset Current  
±0.5  
±0.7  
μA  
CIN  
Input Capacitance  
Input Resistance  
2.5  
6
pF  
RIN  
MΩ  
CMVR  
CMRR  
AOL  
Input Voltage Range  
−0.2  
81  
3.8  
V
DC, CMRR 78 dB  
Common Mode Rejection Ratio VCM Stepped from −0.1V to 3.7V  
98  
103  
86  
dB  
Open Loop Gain  
92  
RL = 1 k, VOUT = 4.6V to 0.4V  
RL = 150Ω, VOUT = 4.4V to 0.6V  
dB  
80  
Output DC Characteristics  
RL = 1 kto V+/2  
RL =150Ω to V+/2  
RL = 1 kto V+/2  
RL =150Ω to V+/2  
RL = 150Ω to V−  
RL = 1 kto V+/2  
RL =150Ω to V+/2  
RL = 1 kto V+/2  
RL =150Ω to V+/2  
RL = 150Ω to V−  
VO  
Output Swing High (LMH6611)  
(Voltage from V+ Supply Rail)  
76  
195  
74  
90  
93  
239  
256  
Output Swing Low (LMH6611)  
(Voltage from VSupply Rail)  
92  
98  
193  
48  
243  
265  
60  
64  
mV  
Output Swing High (LMH6612)  
(Voltage from V+ Supply Rail)  
75  
86  
91  
195  
77  
223  
241  
Output Swing Low (LMH6612)  
(Voltage from VSupply Rail)  
88  
98  
202  
49  
234  
261  
58  
64  
IOUT  
RO  
Linear Output Current  
Output Resistance  
VOUT = V+/2 (Note 6)  
±100  
0.07  
mA  
f = 1 MHz  
Enable Pin Operation  
Enable High Voltage Threshold Enabled (Note 9)  
Enable Pin High Current VDISABLE = 5V  
Enable Low Voltage Threshold Disabled (Note 9)  
3.0  
V
µA  
V
1.2  
2.0  
Enable Pin Low Current  
Turn-On Time  
VDISABLE = 0V  
2.8  
20  
60  
µA  
ns  
ns  
ton  
toff  
Turn-Off Time  
5
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Symbol  
Parameter  
Condition  
Min  
Typ  
Max  
Units  
(Note 8) (Note 7) (Note 8)  
Power Supply Performance  
PSRR  
IS  
Power Supply Rejection Ratio  
DC, VCM = 0.5V, VS = 2.7V to 11V  
81  
96  
dB  
mA  
μA  
Supply Current (LMH6611)  
3.2  
3.6  
4.0  
RL = ∞  
Supply Current (LMH6612)  
(per channel)  
3.2  
3.7  
4.25  
RL = ∞  
ISD  
Disable Shutdown Current  
(LMH6611)  
DISABLE = 0V  
120  
162  
±5V Electrical Characteristics  
Unless otherwise specified, all limits are guaranteed for TJ = +25°C, V+ = 5V, V= −5V, VS = V+ – V, DISABLE = 5V, VCM = VO  
=
0V, AV = +1, RF = 0Ω, when AV +1 then RF = 560Ω, RL = 1 kΩ. Boldface limits apply at temperature extremes.  
Symbol  
Parameter  
Condition  
Min  
Typ  
Max  
Units  
(Note 8) (Note 7) (Note 8)  
Frequency Domain Response  
SSBW  
GBW  
–3 dB Bandwidth Small Signal  
365  
110  
AV = 1, RL = 1 k, VOUT = 0.2 VPP  
MHz  
MHz  
AV = 2, −1, RL = 1 k, VOUT = 0.2 VPP  
Gain Bandwidth  
(LMH6611)  
115  
135  
AV = 10, RF = 2 k, RG = 221Ω, RL = 1 kΩ,  
VOUT = 0.2 VPP  
Gain Bandwidth  
(LMH6612)  
130  
AV = 10, RF = 2 k, RG = 221Ω, RL = 1 kΩ,  
VOUT = 0.2 VPP  
LSBW  
Peak  
−3 dB Bandwidth Large Signal  
85  
87  
AV = 1, RL = 1 k, VOUT = 2 VPP  
AV = 2, RL = 150Ω, VOUT = 2 VPP  
AV = 1  
MHz  
dB  
Peaking  
0.01  
92  
0.1  
dBBW  
0.1 dB Bandwidth  
AV = 1, VOUT = 0.5 VPP, RL = 1 kΩ  
65  
AV = 2, VOUT = 0.5 VPP, RL = 1 kΩ  
RF = RG = 750Ω  
MHz  
45  
AV = 2, VOUT = 2 VPP, RL = 150Ω,  
RF = RG = 680Ω  
DG  
DP  
Differential Gain  
AV = 2, 4.43 MHz, 0.6V < VOUT < 2V,  
RL = 150Ω to V+/2  
0.05  
0.05  
%
Differential Phase  
AV = 2, 4.43 MHz, 0.6V < VOUT < 2V,  
RL = 150Ω to V+/2  
deg  
Time Domain Response  
tr/tf  
Rise & Fall Time  
Slew Rate  
2V Step, AV = 1  
2V Step, AV = 1  
2V Step, AV = −1  
2V Step, AV = −1  
3.5  
460  
60  
ns  
SR  
V/μs  
ts_0.1  
ts_0.01  
0.1% Settling Time  
0.01% Settling Time  
ns  
100  
Noise and Distortion Performance  
SFDR  
Spurious Free Dynamic Range fC = 100 kHz, AV = 2, VOUT = 2 VPP  
fC = 1 MHz, AV = 2, VOUT = 2 VPP  
102  
100  
81  
dBc  
fC = 5 MHz, AV = 2, VOUT = 2 VPP  
en  
in  
Input Voltage Noise  
Input Current Noise  
f = 100 kHz  
10  
nV/  
pA/  
dB  
f = 100 kHz  
2
CT  
Crosstalk  
f = 5 MHz, VIN = 2 VPP  
71  
(LMH6612)  
www.national.com  
6
Symbol  
Parameter  
Condition  
Min  
Typ  
Max  
Units  
(Note 8) (Note 7) (Note 8)  
Input DC Performance  
VOS  
Input Offset Voltage  
(LMH6611)  
VCM = −4.5V  
VCM = −4.5V  
(Note 5)  
0.074  
0.095  
0.4  
±0.600  
±1.1  
mV  
µV/°C  
μA  
Input Offset Voltage  
(LMH6612)  
±0.750  
±1.4  
TCVOS  
Input Offset Voltage Average  
Drift  
IB  
Input Bias Current  
VCM = −4.5V  
−6.5  
0.01  
−10.1  
−11.1  
IO  
Input Offset Current  
±0.5  
±0.7  
μA  
CIN  
Input Capacitance  
Input Resistance  
2.5  
6
pF  
RIN  
MΩ  
CMVR  
CMRR  
AOL  
Input Voltage Range  
−5.2  
81  
3.8  
V
DC, CMRR 81 dB  
Common Mode Rejection Ratio VCM Stepped from −5.1V to 3.7V  
98  
103  
87  
dB  
Open Loop Gain  
96  
RL = 1 k, VOUT = +4.6V to −4.6V  
RL = 150Ω, VOUT = +4.3V to −4.3V  
dB  
80  
Output DC Characteristics  
VO  
Output Swing High (LMH6611)  
(Voltage from V+ Supply Rail)  
107  
339  
103  
332  
54  
125  
130  
RL = 1 kto GND  
RL = 150Ω to GND  
RL = 1 kto GND  
RL = 150Ω to GND  
RL = 150Ω to V−  
402  
433  
Output Swing Low (LMH6611)  
(Voltage from VSupply Rail)  
123  
132  
404  
445  
70  
74  
mV  
Output Swing High (LMH6612)  
(Voltage from V+ Supply Rail)  
107  
340  
108  
348  
56  
118  
125  
RL = 1 kto GND  
RL = 150Ω to GND  
RL = 1 kto GND  
RL = 150Ω to GND  
RL = 150Ω to V−  
375  
407  
Output Swing Low (LMH6612)  
(Voltage from VSupply Rail)  
120  
135  
389  
434  
66  
74  
IOUT  
RO  
Linear Output Current  
Output Resistance  
VOUT = GND (Note 6)  
±120  
0.07  
mA  
f = 1 MHz  
Enable Pin Operation  
Enable High Voltage Threshold Enabled (Note 9)  
Enable Pin High Current VDISABLE = +5V  
Enable Low Voltage Threshold Disabled (Note 9)  
0.5  
V
µA  
V
17.0  
−0.5  
Enable Pin Low Current  
Turn-On Time  
VDISABLE = −5V  
18.6  
19  
µA  
ns  
ns  
ton  
toff  
Turn-Off Time  
60  
7
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Symbol  
Parameter  
Condition  
Min  
Typ  
Max  
Units  
(Note 8) (Note 7) (Note 8)  
Power Supply Performance  
PSRR  
IS  
Power Supply Rejection Ratio  
DC, VCM = −4.5V, VS = 2.7V to 11V  
81  
96  
dB  
mA  
μA  
Supply Current (LMH6611)  
3.3  
3.8  
4.4  
RL = ∞  
Supply Current (LMH6612)  
(per channel)  
3.45  
160  
4.05  
4.85  
RL = ∞  
ISD  
Disable Shutdown Current  
(LMH6611)  
DISABLE = −5V  
212  
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is  
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.  
Note 2: Human Body Model, applicable std. MIL-STD-883, Method 3015.7. Machine Model, applicable std. JESD22-A115-A (ESD MM std. of JEDEC)  
Field-Induced Charge-Device Model, applicable std. JESD22-C101-C (ESD FICDM std. of JEDEC).  
Note 3: The maximum power dissipation is a function of TJ(MAX), θJA. The maximum allowable power dissipation at any ambient temperature is  
PD = (TJ(MAX)) – TA)/ θJA. All numbers apply for packages soldered directly onto a PC Board.  
Note 4: Boldface limits apply to temperature range of −40°C to 125°C  
Note 5: Voltage average drift is determined by dividing the change in VOS by temperature change.  
Note 6: Do not short circuit the output. Continuous source or sink currents larger than the IOUT typical are not recommended as they may damage the part.  
Note 7: Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary over time and will  
also depend on the application and configuration. The typical values are not tested and are not guaranteed on shipped production material.  
Note 8: Limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlations using the Statistical Quality  
Control (SQC) method.  
Note 9: This parameter is guaranteed by design and/or characterization and is not tested in production.  
Connection Diagrams  
6-Pin TSOT23  
8-Pin SOIC  
30033601  
Top View  
30033678  
Top View  
Ordering Information  
Package  
Part Number  
LMH6611MK  
LMH6611MKE  
LMH6611MKX  
LMH6612MA  
LMH6612MAX  
Package Marking  
Transport Media  
NSC Drawing  
1k Units Tape and Reel  
250 Units Tape and Reel  
3k Units Tape and Reel  
95 Rail/Units  
6-Pin TSOT23  
AX4A  
MK06A  
M08A  
8-Pin SOIC  
LMH6612MA  
2.5k Units Tape and Reel  
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8
 
 
 
 
 
 
 
 
 
Typical Performance Characteristics At TJ = 25°C, AV = +1 (RF = 0Ω), otherwise RF = 560Ω for  
AV +1, unless otherwise specified.  
Closed Loop Frequency Response for  
Various Supplies  
Closed Loop Frequency Response for  
Various Supplies  
30033624  
30033625  
Closed Loop Frequency Response for  
Various Supplies  
Closed Loop Frequency Response for  
Various Supplies (Gain = +2)  
30033604  
30033605  
Closed Loop Gain vs. Frequency for  
Various Temperatures  
Closed Loop Gain vs. Frequency for  
Various Temperatures  
30033654  
30033655  
9
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Closed Loop Gain vs. Frequency for  
Various Gains  
Large Signal Frequency Response  
30033630  
30033623  
Large Signal Frequency Response  
±0.1 dB Gain Flatness for Various Supplies  
30033626  
30033631  
±0.1 dB Gain Flatness for Various Supplies  
±0.1 dB Gain Flatness for Various Supplies  
30033606  
30033627  
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10  
±0.1 dB Gain Flatness for Various Supplies  
±0.1 dB Gain Flatness for Various Supplies (Gain = +2)  
30033675  
30033607  
Small Signal Frequency Response with  
Various Capacitive Load  
Small Signal Frequency Response with  
Capacitive Load and Various RISO  
30033608  
30033609  
HD2 and HD3 vs. Frequency and Supply Voltage  
HD2 and HD3 vs. Frequency and Load  
30033653  
30033650  
11  
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HD2 and HD3 vs. Common Mode Voltage  
HD2 and HD3 vs. Common Mode Voltage  
30033677  
30033681  
HD2 vs. Frequency and Gain  
HD3 vs. Frequency and Gain  
30033651  
30033652  
Open Loop Gain and Phase  
HD2 vs. Output Swing  
30033682  
30033676  
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12  
HD3 vs. Output Swing  
HD2 vs. Output Swing  
HD3 vs. Output Swing  
HD2 vs. Output Swing  
30033683  
30033693  
HD3 vs. Output Swing  
30033694  
30033684  
Settling Time vs. Input Step Amplitude  
30033686  
30033685  
13  
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Settling Time vs. Input Step Amplitude  
Input Noise vs. Frequency  
30033687  
30033674  
VOS vs. VOUT  
VOS vs. VOUT  
30033661  
30033668  
VOS vs. VCM  
VOS vs. VS  
30033660  
30033658  
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14  
VOS vs. IOUT  
VOS Distribution  
30033669  
30033672  
IB vs. VS  
IS vs. VS  
30033657  
30033659  
VOUT vs. VS  
VOUT vs. VS  
30033690  
30033691  
15  
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VOUT vs. VS  
Closed Loop Output Impedance vs. Frequency AV = +1  
30033696  
30033671  
Circuit for Positive (+) PSRR Measurement  
+PSRR vs. Frequency  
30033688  
30033633  
Circuit for Negative (−) PSRR Measurement  
−PSRR vs. Frequency  
30033689  
30033634  
www.national.com  
16  
CMRR vs. Frequency  
Small Signal Step Response  
Small Signal Step Response  
Crosstalk vs. Frequency  
Small Signal Step Response  
Small Signal Step Response  
30033632  
30033697  
30033610  
30033611  
30033612  
30033614  
17  
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Small Signal Step Response  
Small Signal Step Response  
Small Signal Step Response  
Small Signal Step Response  
30033615  
30033616  
Small Signal Step Response  
30033617  
30033618  
Large Signal Step Response  
30033619  
30033613  
www.national.com  
18  
Large Signal Step Response  
Overload Recovery Response  
30033620  
30033621  
IS vs. VDISABLE  
30033656  
19  
www.national.com  
Application Information  
The LMH6611 and LMH6612 are based on National  
Semiconductor’s proprietary VIP10 dielectrically isolated  
bipolar process. This device family architecture features the  
following:  
Complimentary bipolar devices with exceptionally high ft  
(8 GHz) even under low supply voltage (2.7V) and low  
bias current.  
Common emitter push-push output stage. This  
architecture allows the output to reach within millivolts of  
either supply rail.  
Consistent performance with little variation from any  
supply voltage (2.7V - 11V) for the most important  
specifications (e.g. BW, SR, IOUT.)  
Significant power saving compared to competitive devices  
on the market with similar performance.  
30033639  
With 3V supplies and a common mode input voltage range  
that extends beyond either supply rail, the LMH6611 is well  
suited to many low voltage/low power applications. Even with  
3V supplies, the −3 dB BW (at AV = +1) is typically 305 MHz.  
FIGURE 2. Input Equivalent Circuit During Shutdown  
When the LMH6611 is shutdown, there may be current flow  
through the internal diodes shown, caused by input potential,  
if present. This current may flow through the external feed-  
back resistor and result in an apparent output signal. In most  
shutdown applications the presence of this output is incon-  
sequential. However, if the output is “forced” by another de-  
vice, the other device will need to conduct the current  
described in order to maintain the output potential.  
The LMH6611 and LMH6612 are designed to avoid output  
phase reversal. With input overdrive, the output is kept near  
the supply rail (or as close to it as mandated by the closed  
loop gain setting and the input voltage). Figure 1 shows the  
input and output voltage when the input voltage significantly  
exceeds the supply voltages.  
To keep the output at or near ground during shutdown when  
there is no other device to hold the output low, a switch using  
a transistor can be used to shunt the output to ground.  
SELECTION OF RF AND EFFECT ON STABILITY AND  
PEAKING  
The peaking of the LMH6611 depends on the value of the  
RF. From the graph shown in Figure 3, as the RF value in-  
creases, the peaking increases.  
For AV = 2, at RF = 1 k, the −3 dB bandwidth is 113 MHz  
and peaking is about 0.6 dB whereas at RF = 665Ω, the −3  
dB bandwidth is about 110 MHz and peaking is 0 dB. RF and  
the input capacitance form a pole in the amplifier’s response.  
If the time constant is too big, it will cause peaking and ringing.  
Except for AV = 1 when RF should be 0, across all other gain  
settings it is recommended that RF remain between 500and  
1 kto ensure optimum performance.  
30033622  
FIGURE 1. Input and Output Shown with CMVR Exceeded  
If the input voltage range is exceeded by more than a diode  
drop beyond either rail, the internal ESD protection diodes will  
start to conduct. The current flow in these ESD diodes should  
be externally limited.  
SHUTDOWN CAPABILITY AND TURN ON/OFF  
BEHAVIOR  
The LMH6611 can be shutdown by connecting the  
DISABLE pin to a voltage 0.5V below the supply midpoint  
which will reduce the supply current to typically 120 µA. The  
DISABLE pin is “active low” and can be connected through a  
resistor to V+ or left floating for normal operation. Shutdown  
is guaranteed when the DISABLE pin is 0.5V below the supply  
midpoint at any operating supply voltage and temperature.  
Typical turn on time is 20 ns and the turn off time is 60 ns.  
In the shutdown mode, essentially all internal device biasing  
is turned off in order to minimize supply current flow and the  
output goes into high impedance mode. During shutdown, the  
input stage has an equivalent circuit as shown in Figure 2.  
30033692  
FIGURE 3. Closed Loop Gain vs. Frequency and RF = RG  
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20  
 
 
 
quired to drive the input of the ADC. To minimize the droop in  
the input voltage, external shunt capacitance (CL) should be  
about ten times larger than the internal input capacitance of  
the ADC and external series resistance (RL) should be large  
enough to maintain the phase delay at the output of the op  
amp and hence maintain the stability (See Figure 4) . Most  
applications benefit from the inclusion of a series isolation re-  
sistor connected between the op amp output and ADC input.  
This series resistor helps to limit the output current of the op  
amp. The value chosen for this series resistor is very impor-  
tant, as a higher value will increase the load impedance seen  
by the op amp and improve the total harmonic distortion  
(THD) performance of the op amp; however, the ADC prefers  
a low impedance source driving it. Thus, the optimum value  
for this series resistor must be found so that it will offer the  
best performance in terms of THD, SNR and SFDR of the  
combined op amp and ADC.  
RF = RG  
665  
f −3 dB (MHz)  
Peaking (dB)  
110  
113  
0
1000  
0.6  
MINIMIZING NOISE  
With a low input voltage noise of 10 nV/  
rent noise of 2 pA  
and an input cur-  
the LMH6611 and LMH6612 are suit-  
able for high accuracy applications. Still being able to reduce  
the frequency band of operation of the various noise sources  
(i.e. op amp noise voltage, resistor thermal noise, input noise  
current) can further improve the noise performance of a sys-  
tem. In a non-inverting amplifier configuration inserting a  
capacitor, CG, in series with the gain setting resistor, RG, will  
reduce the gain of the circuit below frequency,  
f =  
1/2πRGCG. This can be set to reduce the contribution of noise  
from the 1/f region. Alternatively applying a feedback capac-  
itor, CF, in parallel with the feedback resistor, RF, will introduce  
a pole into your system at f = 1/2πRFCF and create a low pass  
filter. This filter can be set to reduce high frequency noise and  
harmonics. Finally remember to keep resistor values as small  
as possible for a given application in order to reduce resistor  
thermal noise.  
Important Specifications of Op Amp and ADC  
When interfacing an ADC with an op amp it is imperative to  
understand the specifications that are important to get the  
expected performance results. Modern ADC AC specifica-  
tions such as THD, SNR, settling time and SFDR are critical  
for filtering, test and measurement, video and reconstruction  
applications. The high performance op amp’s settling time,  
THD, and noise performance must be better than that of the  
ADC it is driving to maintain the proper system accuracy with  
minimal or no error.  
POWER SUPPLY BYPASS  
Since the LMH6611 and LMH6612 are wide bandwidth am-  
plifiers, proper power supply bypassing is critical for optimum  
performance. Improper power supply bypassing can result in  
large overshoot, ringing or oscillation. 0.1 μF capacitors  
should be connected from the supply pins, V+ and V, to  
ground, as close to the device as is practical. Additionally, a  
10 μF electrolytic capacitor should be connected from both  
supply pins to ground reasonably close to the device. Finally,  
near the device a 0.1 μF ceramic capacitor between the sup-  
plies will provide the best harmonic distortion performance.  
Some system applications require low THD, low SFDR and  
wide dynamic range (SNR), whereas some system applica-  
tions require high SNR and they may sacrifice THD and SFDR  
to focus on the noise performance.  
Noise is a very important specification for both the op amp  
and the ADC. There are three main sources of noise that  
contribute to the overall performance of the ADC: Quantiza-  
tion noise, noise generated by the ADC itself (particularly at  
higher frequencies) and the noise generated by the applica-  
tion circuit. The impedance of the input source affects the  
noise performance of the op amp. Theoretically, an ADC’s  
signal to noise ratio (SNR) can be found from the equation:  
INTERFACING HIGH PERFORMANCE OP AMPS WITH  
ADCs  
These amplifiers are designed for ease of use in a wide range  
of applications requiring high speed, low supply current, low  
noise, and the ability to drive complex ADC and video loads.  
SNR (in dB) = 6.02*N+1.72  
The source that drives the modern high resolution analog-to-  
digital converters (ADCs) sees a high frequency AC load and  
a DC load of a few hundred ohms or more. Thus, a high per-  
formance op amp with high input impedance of a few mega  
ohms and low output impedance would be an ideal choice as  
an input ADC driver. The LMH6611/LMH6612 have the low  
output impedance of 0.07at f = 1 MHz. The ADC driver acts  
as a buffer and a low pass filter to reduce the overall system  
noise. To utilize the full dynamic range of the ADC, the ADC  
input has to be driven to full scale input voltage.  
where N is the resolution of the ADC. For example, according  
to this equation a 12-bit ADC has an SNR of 74 dB. However,  
the practical SNR number would be about 72 dB. In order to  
achieve better SNR, the ADC driver noise should be as small  
as possible. The LMH6611/LMH6612 have the low voltage  
noise of only 10 nV/  
.
The combined settling time of the op amp and the ADC must  
be within 1 LSB. The 0.01% settling time of the LMH6611/  
LMH6612 is 100 ns.  
As signals travel through the traces of a printed circuit board  
(PCB) and long cables, system noise accumulates in the sig-  
nals and a differential ADC rejects any signals noise that  
appears as a common mode voltage. There are a couple of  
advantages to using differential signals rather than single-  
ended signals. First, differential signals double the dynamic  
range of the ADC and second, they offer better harmonic dis-  
tortion performance. There are several ways to produce dif-  
ferential signals from a dual op amp configuration. One  
method is to utilize the single-ended to differential conversion  
technique and the other is the differential to differential con-  
version technique. The first method requires a single input  
source and the second method requires differential input  
source.  
The ADC driver’s THD should be inherently lower than that of  
the ADC. The LMH6611/LMH6612 have an SFDR of 96 dBc  
at 2 VPP output and 1 MHz input frequency.  
Signal to Noise and Distortion (SINAD) is a parameter which  
is the combination of the SNR and THD specifications. SINAD  
is defined as the RMS value of the output signal to the RMS  
value of all of the other spectral components below half the  
clock frequency, including harmonics but excluding DC. It can  
be calculated from SNR and THD according to the equation:  
A real world input source can have non-ideal impedance thus  
the buffer amplifier, with very low output impedance, is re-  
21  
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Because SINAD compares all undesired frequency compo-  
nents with the input frequency, it is an overall measure of an  
ADC’s dynamic performance. The following sections will dis-  
cuss the three different ADC driver architectures in detail.  
uration is preferred over the non-inverting configuration, as it  
offers more linear output response. Table 1 shows the per-  
formance data of the LMH6611 combined with the AD-  
C121S101. The ADC driver’s cutoff frequency of 500 kHz is  
found from the equation:  
SINGLE TO SINGLE ADC DRIVER  
This architecture has a single-ended input source connected  
to the input of the op amp and the single-ended output of the  
op amp is then fed to the single-ended input of the ADC. The  
low noise of only 10 nV/  
and a wide bandwidth of 345 MHz  
make the LMH6611 an excellent choice for driving the 12-bit  
ADC121S101 500 KSPS to 1 MSPS ADC, which has a suc-  
cessive approximation architecture with internal sample and  
hold circuits. Figure 2 shows the schematic of the LMH6611  
in a 2nd order multiple-feedback with gain of −1 (inverting)  
configuration, driving an ADC121S101. The inverting config-  
The op amp’s gain is set by the equation:  
30033629  
FIGURE 4. Single to Single ADC Driver  
TABLE 1. Performance of the LMH6611 Combined with the ADC121S101  
Amplifier  
Output/ADC Input  
SINAD  
(dB)  
SNR  
(dB)  
71.6  
THD  
(dB)  
SFDR  
(dBc)  
77.6  
ENOB  
Notes  
4
70.2  
−75.7  
11.4  
ADC121S101 @ f = 200 kHz  
When the op amp and the ADC are using the same supply, it  
is important that both devices are well bypassed. A 0.1 µF  
ceramic capacitor and a 10 µF tantalum capacitor should be  
located as close as possible to each supply pin. A sample  
layout is shown in Figure 5. The 0.1 µF capacitors (C13 and  
C6) and the 10 µF capacitors (C11 and C5) are located very  
close to the supply pins of the LMH6611 and the AD-  
C121S101.  
Place ADC and amplifier as close together as possible.  
Put the supply bypassing capacitors as close as possible  
to the device (<1”).  
Utilize surface mount instead of through-hole components  
and ground and power planes.  
Keep the traces short where possible.  
Use terminated transmission lines for long traces.  
The following are recommendations for the design of PCB  
layout in order to obtain the optimum high frequency perfor-  
mance:  
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22  
 
 
30033640  
FIGURE 5. LMH6611 and ADC121S101 Layout  
SINGLE-ENDED TO DIFFERENTIAL ADC DRIVER  
up at the non-inverting inputs of both op amps U1 and U2.  
This configuration produces differential ±2.5 VPP output sig-  
nals, when the single-ended input signal of 0 to VREF is AC  
coupled into the non-inverting terminal of the op amp and  
each non-inverting terminal of the op amp is biased at the mid-  
scale of 2.5V. The two output RC anti-aliasing filters are used  
between both the outputs of U1 and U2 and the input of the  
ADC121S625 to minimize the effect of undesired high fre-  
quency noise coming from the input source. Each RC filter  
has the cutoff frequency of approximately 22 MHz.  
The single-ended to differential ADC driver in Figure 3 utilizes  
an LMH6612 dual op amp to buffer a single-ended source to  
drive an ADC with differential inputs. One of the op amps is  
configured as a unity gain buffer that drives the inverting  
(IN−) input of the op amp U2 and non-inverting (IN+) input of  
the ADC121S625. U2 inverts the input signal and drives the  
inverting input of the ADC121S625. The ADC driver is con-  
figured for a gain of +2 to reduce the noise without sacrificing  
THD performance. The common mode voltage of 2.5V is set  
30033680  
FIGURE 6. Single-Ended to Differential ADC Driver  
23  
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The performance of the LMH6612 with the ADC121S625 is  
shown in Table 2.  
TABLE 2. Performance of the LMH6612 Combined with the ADC121S625  
Amplifier  
Output/ADC Input  
SINAD  
(dB)  
SNR  
(dB)  
69  
THD  
(dB)  
SFDR  
(dBc)  
75.1  
ENOB  
Notes  
2.5  
68.8  
−81.5  
11.2  
ADC121S625 @ f = 20 kHz  
DIFFERENTIAL TO DIFFERENTIAL ADC DRIVER  
single ADC drivers. Each output from these drivers goes to a  
separate input of the differential ADC. Here, each single to  
single ADC driver uses the same components and is config-  
ured for a gain of -1 (inverting).  
The LMH6612 dual op amp can be configured as a differential  
to differential ADC driver to buffer a differential source to a  
differential input ADC as shown in Figure 7. The differential  
to differential ADC driver can be formed using two single to  
30033642  
FIGURE 7. Differential to Differential ADC Driver  
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24  
 
 
The following table summarizes the performance of the  
LMH6612 combined with the ADC121S625 at two different  
frequencies. In order to utilize the full dynamic range of the  
ADC, the maximum input of 2.5 VPP is applied to the ADC  
input. Figure 8 shows the FFT plot of the LMH6612 and AD-  
C121S625 combination tested at f = 20 kHz input frequency.  
TABLE 3. Performance of the LMH6612 Combined with the ADC121S625  
Amplifier  
Output/ADC Input  
SINAD  
(dB)  
SNR  
(dB)  
72.3  
72.2  
THD  
(dB)  
SFDR  
(dBc)  
92.1  
ENOB  
Notes  
2.5  
2.5  
72.2  
−87.7  
−87.8  
11.7  
11.7  
ADC121S625 @ f = 20 kHz  
ADC121S625 @ f = 200 kHz  
72.2  
90.8  
30033673  
FIGURE 8. The FFT Plot of Differential to Differential ADC Driver  
25  
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DC LEVEL SHIFTING  
Often a signal must be both amplified and level shifted while  
using a single supply for the op amp. The circuit in Figure 9  
can do both of these tasks. The procedure for specifying the  
resistor values is as follows.  
1. Determine the input voltage.  
2. Calculate the input voltage midpoint, VINMID = VINMIN  
(VINMAX – VINMIN)/2.  
+
3. Determine the output voltage needed.  
4. Calculate the output voltage midpoint, VOUTMID  
VOUTMIN + (VOUTMAX – VOUTMIN)/2.  
=
5. Calculate the gain needed, gain = (VOUTMAX – VOUTMIN)/  
(VINMAX – VINMIN  
)
6. Calculate the amount the voltage needs to be shifted  
30033648  
from input to output, ΔVOUT = VOUTMID – gain x VINMID  
.
7. Set the supply voltage to be used.  
FIGURE 9. DC Level Shifting  
8. Calculate the noise gain, noise gain = gain + ΔVOUT/VS.  
9. Set RF.  
The following example is for a VIN of 0V to 1V with a VOUT of  
2V to 4V.  
10. Calculate R1, R1 = RF/gain.  
11. Calculate R2, R2 = RF/(noise gain-gain).  
12. Calculate RG, RG= RF/(noise gain – 1).  
1. VIN = 0V to 1V  
2. VINMID = 0V + (1V – 0V)/2 = 0.5V  
3. VOUT = 2V to 4V  
Check that both the VIN and VOUT are within the voltage  
ranges of the LMH6611.  
4. VOUTMID = 2V + (4V – 2V)/2 = 3V  
5. Gain = (4V – 2V)/(1V – 0V) = 2  
6.  
ΔVOUT = 3V – 2 x 0.5V = 2  
7. For the example the supply voltage will be +5V.  
8. Noise gain = 2 + 2/5V = 2.4  
9. RF = 2 kΩ  
10. R1 = 2 k/2 = 1 kΩ  
11. R2 = 2 kΩ/(2.4-2) = 5 kΩ  
12. RG = 2 kΩ/(2.4 – 1) = 1.43 kΩ  
4th ORDER MULTIPLE FEEDBACK LOW-PASS FILTER  
of +1 and a −3 dB point of 1 MHz. Values can be determined  
by using the WEBENCH® Active Filter Designer found at  
www.amplifiers.national.com.  
Figure 10 shows the LMH6612 used as the amplifier in a mul-  
tiple feedback low pass filter. This filter is set up to have a gain  
30033628  
FIGURE 10. 4th Order Multiple Feedback Low-Pass Filter  
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26  
 
 
CURRENT SENSE AMPLIFIER AND OPTIMIZING  
ACCURACY IN PRECESION APPLICATIONS  
current by using larger values of gain (RF). The total capaci-  
tance (CT) on the inverting terminal of the op amp includes  
the photodiode capacitance (CPD) and the input capacitance  
of the op amp (CIN). This total capacitance (CT) plays an im-  
portant role in the stability of the circuit. The noise gain of this  
circuit determines the stability and is defined by:  
With it’s rail-to-rail output capability, low VOS, and low IB the  
LMH6611 is an ideal choice for a current sense amplifier ap-  
plication. Figure 11 shows the schematic of the LMH6611 set  
up in a low-side sense configuration which provides a con-  
version gain of 2V/A. Voltage error due to VOS can be calcu-  
lated to be VOS x (1 + RF/RG) or 0.6 mV x 21 = 12.6 mV.  
Voltage error due to IO is IO x RF or 0.5 µA x 1 kΩ = 0.5 mV.  
Hence worst case total voltage error is 12.6 mV + 0.5 mV or  
13.1 mV which translates into a current error of 13.1 mV/(2 V/  
A) = 6.55 mA.  
(1)  
(2)  
This circuit employs DC source resistance matching at the  
two input terminals in order to minimize the output DC error  
caused by input bias current. Another technique to reduce  
output offset in a non-inverting amplifier configuration is to in-  
troduce a DC offset current into the inverting input of the  
amplifier. To ensure minimal impact on frequency response  
be sure to inject the DC offset current through large resistors.  
Conversely if optimizing an inverting amplifier configuration  
simply apply offset adjustment to the non-inverting input.  
30033665  
30033641  
FIGURE 13. Bode Plot of Noise Gain Intersecting with Op  
Amp Open Loop Gain  
FIGURE 11. Current Sense Amplifier  
TRANSIMPEDANCE AMPLIFIER  
Figure 13 shows the bode plot of the noise gain intersecting  
the op amp open loop gain. With larger values of gain, CT and  
RF create a zero in the transfer function. At higher frequencies  
the circuit can become unstable due to excess phase shift  
around the loop.  
By definition, a photodiode produces either a current or volt-  
age output from exposure to a light source. A Tran-  
simpedance Amplifier (TIA) is utilized to convert this low-level  
current to a usable voltage signal. The TIA often will need to  
be compensated to insure proper operation.  
A pole at fP in the noise gain function is created by placing a  
feedback capacitor (CF) across RF. The noise gain slope is  
flattened by choosing an appropriate value of CF for optimum  
performance.  
Theoretical expressions for calculating the optimum value of  
CF and the expected −3 dB bandwidth are:  
(3)  
(4)  
Equation 4 indicates that the −3 dB bandwidth of the TIA is  
inversely proportional to the feedback resistor. Therefore, if  
the bandwidth is important then the best approach would be  
to have a moderate transimpedance gain stage followed by a  
broadband voltage gain stage.  
30033662  
FIGURE 12. Photodiode Modeled with Capacitance  
Elements  
Table 4 shows the measurement results of the LMH6611 with  
different photodiodes having various capacitances (CPD) and  
a feedback resistance (RF) of 1 kΩ.  
Figure 12 shows the LMH6611 modeled with photodiode and  
the internal op amp capacitances. The LMH6611 allows cir-  
cuit operation of a low intensity light due to its low input bias  
27  
www.national.com  
 
 
 
 
TABLE 4. TIA (Figure 1) Compensation and Performance Results  
CPD  
(pF)  
22  
CT  
(pF)  
24  
CF CAL  
(pF)  
CF USED  
(pF)  
5.6  
8
f −3 dB CAL  
(MHz)  
29.3  
f −3 dB MEAS  
(MHz)  
27.1  
Peaking  
(dB)  
0.5  
5.42  
47  
49  
7.75  
20.5  
21  
0.5  
100  
222  
330  
102  
224  
332  
11.15  
20.39  
20.2  
12  
14.2  
15.2  
0.5  
18  
9.6  
10.7  
0.5  
22  
7.9  
9
0.8  
Note:  
GBWP = 130 MHz  
CT = CPD + CIN  
CIN = 2 pF  
VS = ±2.5V  
Figure 14 shows the frequency response for the various pho-  
todiodes in Table 4.  
noise voltage, feedback resistor thermal noise, input noise  
current, photodiode noise current) do not all operate over the  
same frequency band. Therefore, when the noise at the out-  
put is calculated, this should be taken into account. The op  
amp noise voltage will be gained up in the region between the  
noise gain’s zero and pole (fZ and fP in Figure 13). The higher  
the values of RF and CT, the sooner the noise gain peaking  
starts and therefore its contribution to the total output noise  
will be larger. It is advantageous to minimize CIN by proper  
choice of op amp or by applying a reverse bias across the  
diode but this will be at the expense of excess dark current  
and noise.  
EVALUATION BOARD  
National Semiconductor provides the following evaluation  
board as a guide for high frequency layout and as an aid in  
device testing and characterization. Many of the datasheet  
plots were measured with this board:  
Device  
Package  
Board Part #  
LMH6611MK  
TSOT23  
LMH730216  
30033635  
This evaluation board can be shipped when a device sample  
request is placed with National Semiconductor.  
FIGURE 14. Frequency Response for Various Photodiode  
and Feedback Capacitors  
When analyzing the noise at the output of the TIA, it is im-  
portant to note that the various noise sources (i.e. op amp  
www.national.com  
28  
 
 
Physical Dimensions inches (millimeters) unless otherwise noted  
6-Pin TSOT23  
NS Package Number MK06A  
8-Pin SOIC  
NS Package Number M08A  
29  
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