SW-3911 [TE]
Drivers for GaAs FET Switches and Digital Attenuators; 驱动程序的GaAs FET开关和数字衰减器
| 型号： | SW-3911 |
| 厂家： | 
TE CONNECTIVITY |
| 描述： | Drivers for GaAs FET Switches and Digital Attenuators |
| 文件： | 总4页 (文件大小：83K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Application Note
S2079
Drivers for GaAs FET Switches and Digital Attenuators
Rev. V5
Figure 2 shows a 3-bit digital attenuator. Applying the
correct bias voltage and its complement to any stage
switches the pad for that stage into the RF signal path.
Introduction
Many of M/A-COM's GaAs FET switches and digital
attenuators cannot operate directly with simple TTL or
CMOS logic, but instead require external circuits to
provide appropriate control voltages. This application
note, an update of M539, Drivers for GaAs FET MMIC
Switches and Digital Attenuators, provides information
on M/A-COM's SW-109 and SWD-119 drivers and
other commercially available digital logic IC's for control
of switches and digital attenuators.
GaAs FET’s
GaAs MMIC control devices such as switches and
digital attenuators typically employ Field Effect
Transistors (FET’s). The most common FET is the n-
channel depletion mode device, which has low source-
to-drain resistance in the absence of a gate bias, and
allows a current IDSS to flow. With the application of a
negative gate bias voltage, the electric field below the
gate causes the conduction channel to narrow,
increasing the source-to-drain resistance. The gate
voltage that creates a high enough resistance to reduce
the source-to-drain current to (typically) 1 - 2 percent of
IDSS is known as the pinch-off voltage. For M/A-COM
FET’s,. the pinch-off voltage is typically –2.5 volts. If
the transistor is biased at the extremes, (0 V and –5 V
typically), on and off switching results, providing the
basis for both GaAs MMIC switches and digital
attenuators.
Dual Control Switch Truth Table
Control A Control B RF Common
to RF1
RF Common
to RF2
-5 V
0 V
0 V
On
Off
Off
On
-5 V
Typical complementary logic control voltages:
Logic low
Logic high
0 V to –2 V @ 20 μA max.
-5 V to 40 μA typ. To –8 V @ 200 μ
A max.
Switch Circuit Topology
In switches, FET's are arranged in both series and
shunt configurations. The series FET's provide a
through-path for the on state, while the shunt FET's
provide isolation for the off state. The operation of the
switch requires that series FET's and shunt FET's
associated with each switch state have opposite (or
complementary) conduction states and therefore
Figure 1: Typical Dual Control Switch (SW-239, etc)
opposite (or complementary) gate biases.
For
example, Figure 1 illustrates the operation of a typical
dual control SPST GaAs MMIC switch. If the RF to
RF1 path is on and the RF to RF2 path is off, then
FET's Q2 and Q4 are biased on, while Q1 and Q3 are
biased off.
Figure 2: Digital Attenuator Based on Switched Pads
(AT-230)
Digital attenuators use series/shunt stages with circuit
components that form fixed attenuator pads,
corresponding to digital attenuation bits, switched in or
out of the transmission path, either individually or in
combination. Switches require complementary bias
voltages for each state, while digital attenuators require
complementary bias voltage to activate each bit.
1
• North America Tel: 800.366.2266 • Europe Tel: +353.21.244.6400
Visit www.macomtech.com for additional data sheets and product information.
• India Tel: +91.80.4155721
• China Tel: +86.21.2407.1588
M/A-COM Technology Solutions Inc. and its affiliates reserve the right to make
changes to the product(s) or information contained herein without notice.
Application Note
S2079
Drivers for GaAs FET Switches and Digital Attenuators
Rev. V5
Another consideration in design with switches and
attenuators is the elimination of crosstalk that can arise
Built-in Drivers
Some of M/A-COM's newer switches and attenuators
feature simplified control using CMOS (0 V, 2.7 V) or TTL
(0 V, 5 V) logic, with no need for negative control
voltages.
from RF leakage onto control lines.
Most board
designers take care of this by adding capacitance to
ground on the control lines, shunting any RF energy to
ground. The SW-109 and SWD-119 output buffers can
drive load capacitance up to 25 pF.
The Appendix to this application note lists some popular
M/A-COM switches. The SW-277, SW-349, SW-394,
and SW-399 include level shifting components for
compatibility with positive CMOS or TTL control voltages,
but these switches still require complementary control
logic. The SW-335, SW65-0xxx series and related
switches incorporate a CMOS driver circuit in the same
package, along with the GaAs switching elements, for
true single line control. Many future switches from M/A-
COM will likely incorporate driver circuitry and switching
elements together in small, low cost plastic packages.
Other Circuits as Drivers
You can use TTL and CMOS logic IC's to drive GaAs
FET switches and attenuators. An ideal driver would run
from a single supply voltage, consume little current, and
introduce very little switching delay.
One driver technique that works well floats the channel of
the FET's on the MMIC switch above ground potential
through the addition of pull-up resistors and DC blocking
and bypass capacitors. As shown in Figure 3, the circuit
takes a voltage of 0 VDC, applied to either control port,
and shifts it to -5 VDC at the attached FET gates to turn
them off. A voltage of +5 VDC shifts to 0 VDC at the
FET gates to turn them on.
The AT-226, AT-264, and AT-242 digital attenuators
feature internal level shifting to provide control with a
single CMOS input line for each attenuation bit. The
AT65-0xxx series miniature digital attenuator modules
incorporate CMOS driver circuitry to accomplish this.
SWD-109 & SWD-119 Drivers
M/A-COM's SWD-109 and quad-channel SWD-119
provide the complementary control voltages necessary
for driving GaAs FET switches and digital attenuators
using a single control input per bit. Both the SWD-109
and SWD-119 incorporate buffering stages so that the
drivers will switch with either standard TTL or CMOS
logic level input. The devices employ standard CMOS
analog fabrication techniques for low power
consumption.
The devices consist of input buffers, inverters to
generate complementary logic values, voltage
translators, and output buffers, all designed to allow the
designer the flexibility to optimize switch and attenuator
performance.
To design a board with RF switches and attenuators,
consider that modulation of the source-drain resistance
in the FET's by input RF can lead to output compression
and intermodulation distortion. Although GaAs FET
switches and attenuators will operate well with nominal 0
V and -5 V for control, careful selection of the control
voltages in the ranges of - 8 V < VFEToff < - 5 V, and 0 V <
RF Common
to RF 1
RF Common
to RF 2
Control A Control B
VFETon < 2 V can improve the maximum RF level (P1dB).
With proper selection of positive and negative supply
voltage, the SWD-109 and SWD-119 can both provide
output control voltages in these ranges.
TTL Low
TTL High
TTL High
TTL Low
ON
OFF
ON
OFF
Figure 3: GaAs SPDT Switch with CMOS Driver
2
• North America Tel: 800.366.2266 • Europe Tel: +353.21.244.6400
Visit www.macomtech.com for additional data sheets and product information.
• India Tel: +91.80.4155721
• China Tel: +86.21.2407.1588
M/A-COM Technology Solutions Inc. and its affiliates reserve the right to make
changes to the product(s) or information contained herein without notice.
Application Note
S2079
Drivers for GaAs FET Switches and Digital Attenuators
Rev. V5
M/A-COM's dual control, negative bias switches and
attenuators have intrinsic switching speeds as low as ~ 5
ns. A disadvantage of level shifting by floating the FET's
is that the time constants of the bypass and blocking
capacitors charging through the internal FET gate
resistors will introduce some switching delays. As shown
in the appendix, switches that incorporate level shifting
on-chip typically have switching speeds ranging from
several tens of nanoseconds to microseconds.
This will result in slower switching speed and higher
current consumption compared to the CD54HCT04.
The Texas Instruments SN54HC139 two to 4 line
decoder also works well, as does the CD4041UB quad /
true complement buffer. The CD4041UB provides four
pairs of complementary outputs, and can provide a range
of logic output voltages depending upon the supply
voltage that you choose. With the CD4041UB supplying
a bias of 8 VDC for the logic high, many GaAs FET
switches will operate with a higher P1dB power level,
higher by perhaps 5 or 6 dB.
Figure 3 shows a dual control GaAs FET switch driven
by the Texas Instruments CD54HCT04 high speed
CMOS logic hex inverter, a CERDIP packaged device
that can operate with CMOS logic input levels (0 V, 2.7
V) and drive TTL loads. Driving a dual control switch
stage requires using two gates of the CD54HCT04, one
to generate a buffered output, one to generate its
complement. Each gate in the CD54HCT04 introduces a
switching propagation delay of 20 ns. The DC current
consumption of the entire hex device is less than 1 mA at
+ 5 VDC.
For driver switching speeds less than 10 ns at the
expense of higher current consumption, consider using
an ECL driver such as the Motorola MC10H350 ECL to
TTL translator, as shown in Figure 4. This circuit can
drive the switch directly without the need for level shifting
capacitors and resistors.
When designing with the CD54HCT04 as a driver,
choose the DC blocking capacitors C1, C4, and C5, to
give minimum insertion loss at the lowest desired
operating frequency. Choose the bypass capacitors C2
and C3 to give maximum isolation at the highest desired
operating frequency. Bypass capacitor C6, which has
the same value as C2 and C3, shunts any RF signal
leakage on the DC bias line at the hex inverter to ground.
Use low series resistance, high Q capacitors, such as the
American Technical Ceramic ATC100A series, for the
lowest possible insertion loss.
The resistors R1 and R3 that connect the DC bias to the
switch should have a value in the range of 10 to 50
kilohms to keep RF crosstalk as low as possible. Place
the resistors, capacitors and ground vias as close to the
body of the switch as possible to reduce inductance for
the best RF performance.
Figure 4: MC10H350 for Driving Dual Control
Switches
Conclusion
Other popular logic IC's work well as drivers, depending
upon your requirements for switching speed, DC power
consumption, and RF linearity. Other hex inverters
related to the CD54HCT04 that work well include the
SOIC or plastic DIP packaged CD74HC04 and
CD74HCT04, the slower CD54HC04, and the Fairchild
DM74LS04.
This application note has explained how to control
M/A-COM's GaAs FET switches and digital attenuators
using drivers provided by M/A-COM, or using
commercially available digital logic IC's. The appendix
summarizes M/A-COM's most popular switches and
classifies them by drive requirements. Careful choice of
the switch or digital attenuator and the driver can provide
optimum RF linearity, fast switching speed, low power
consumption and small board footprint.
With a 5 VDC supply voltage, the DM74LS04 provides
output logic voltages of 0.25 V (logic low) and 3.4 V
(logic high). To substitute the pin-compatible DM74SL04
for the CD54HCT04, you will have to add additional pull-
up circuitry connected between the driver and the switch
to raise the logic high to 5 VDC.
3
• North America Tel: 800.366.2266 • Europe Tel: +353.21.244.6400
Visit www.macomtech.com for additional data sheets and product information.
• India Tel: +91.80.4155721
• China Tel: +86.21.2407.1588
M/A-COM Technology Solutions Inc. and its affiliates reserve the right to make
changes to the product(s) or information contained herein without notice.
Application Note
S2079
Drivers for GaAs FET Switches and Digital Attenuators
Rev. V5
Additional Notes:
Appendix
Application Note M537, GaAs MMIC Based Control
Components with Integral Drivers defines performance
parameters for switches and attenuators.
Popular M/A-COM GaAs FET switches
In the following tables, switching speed is the time from
the 50 percent point of the control voltage rise or fall to
the occurrence of 90 percent (on) or 10 percent (off) of
the switched RF level.
1. See Application Note M517, MASW6010 GaAs
SPDT Switch Performance and Driver Circuit
Techniques for additional information on designing
with the SWD-109 and SWD-119 drivers.
2. For pin assignments and supply voltages for the
SWD-109 and SWD-119 single/quad drivers, see
the SWD-109/119 data sheet, available on the M/A-
COM web site at www.macom.com.
Dual Positive Control, Requires Positive Supply
(Includes pull-up components on-chip)
Switching
Speed
Part Number
Type
Package
3. See Application Note M521, Positive Voltage Control
of GaAs MMIC Control Devices for more information
on floating attenuators above ground potential.
4. See Application Note M539, Drivers for GaAs MMIC
Switches and Digital Attenuators for more
SW-277
SW-349
SW-394
SW-399
SPDT
SPST terminated
SPDT
SOIC-8
SOIC-8
SOIC-8
SOT-26
35 ns
2 μs
36 μs
110 μs
SPST
Single Control, Integral Driver, Requires
Positive And Negative Supplies
information on compression and intermodulation
distortion and the operation of the SW-109 and
SWD-119 drivers.
Switching
Speed
5. See manufacturers' data sheets and application
notes for additional information on digital logic IC's.
6. Please contact your M/A-COM sales
representative for information on the latest
switches and attenuators.
Part Number
Type
Package
SW05-0311 SPST, TTL/CMOS in
SW10-0312 SPDT, TTL/CMOS in
SW10-0313 SPDT, TTL/CMOS in
CR-9
CR-9
CR-9
150 ns
150 ns
150 ns
50 ns
50 ns
50 ns
50ns
SW65-0014 SPST, TTL/CMOS in SOIC-24
SW65-0114 SPST, TTL/CMOS in SOIC-24
SW65-0214 SP3T, TTL/CMOS in SOIC-24
SW65-0313 SP2T, TTL/CMOS in SOIC-16
Dual Control Negative Bias
Switching
Speed
Part No.
Type
Package
SW65-0314 SP4T, TTL/CMOS in SOIC-24
SP4T, absorptive,
50 ns
SW-212
SW-214
SW-226
SW-227
SW-239
SW-259
SW-276
SW-279
SW-289
SPST
SPST terminated
SPDT terminated
SPDT
FP-13
FP-13
6 ns
SW65-0440
QSOP-24
50 ns
6 ns
TTL/CMOS in
SW-110
SW-311
SW-312
SW-313
SW-335
SW-224
SW- 225
SPDT, TTL/CMOS in
CR-9
CR-9
CR-9
CR-9
35 ns
12 ns
7 ns
CR-2
6 ns
SPST, TTL.CMOS in
SPDT, TTL/CMOS in
SPD, TTL/CMOS in
CR-2
6 ns
SPDT
SOIC-8
SOIC-8
CR-2
4 ns
18 ns
200 ns
150 ns
150 ns
SPST terminated
SPDT
8 ns
SPDT, TTL /CMOS in SOIC-8
35 ns
35 ns
6 ns
SPDT, TTL in
SPDT, TTL in
TO-5-4
FP-13
SPDT
SOIC-8
SOIC-14
SOIC-8
SOT-26
SOT-26
SOT-26
SOIC-24
SOT-26
SOT-363
MSOP-10
SP4T
Single Control, Integral Driver, Positive Supply
Switching
SW-337, 338 SPDT terminated
10 ns
42 ns
20 ns
8 ns
SW-3911
SW-3921
SW-3951
SW-419
SW-4251
SW-437
SW-439*
SPDT
SPDT
SPDT
SP4T
SPDT
SPDT
SPDT
Part Number
Type
Package
Speed
SW-205
SW-206
SW-215
SW-216
SW-217
SW-233
SW-236
SPDT, TTL in
SPDT, CMOS in
SPST, TTL in
DI-1
DI-1
20 ns
40 ns
20 ns
40 ns
20 ns
20 ns
40 ns
16 ns
~ 20 ns
~ 8 ns
~ 34 ns
DI-1
SPDT, CMOS in
SPDT, TTL in
SPDT, TTL in
SPDT, CMOS in
DI-1
DI-1
FP-16
FP-16
1. Contains no shunt FET’s, hence can operate with positive
control voltages without ground pull-up components if
provided with DC blocking capacitors on all RF lines.
4
• North America Tel: 800.366.2266 • Europe Tel: +353.21.244.6400
• India Tel: +91.80.4155721 • China Tel: +86.21.2407.1588
Visit www.macomtech.com for additional data sheets and product information.
M/A-COM Technology Solutions Inc. and its affiliates reserve the right to make
changes to the product(s) or information contained herein without notice.
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