XRT5894 [EXAR]
Four-Channel E1 Line Interface (3.3V or 5.0V); 四通道E1线路接口（ 3.3V或5.0V ）
| 型号： | XRT5894 |
| 厂家： | 
EXAR CORPORATION |
| 描述： | Four-Channel E1 Line Interface (3.3V or 5.0V) |
| 文件： | 总19页 (文件大小：826K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
XRT5894
Four-Channel E1
Line Interface (3.3V or 5.0V)
March 2000-3
FEATURES
D Compliant with ITU G.703 Pulse Mask Template for
D Logical Inputs Accept either 3.3V or 5.0V Levels
D Ultra-Low Power Dissipation
2.048Mbps (E1) Rates
D Four Independent CEPT Transceivers
D +3.3V or 5.0V Supply Operations
D Supports Differential Transformer Coupled
D Individual Transmit Channel Over Temperature
Receivers and Transmitters
Protection
D On Chip Pulse Shaping for Both 75Ω and 120Ω Line
Drivers
APPLICATIONS
D Compliant with ITU G.775 LOS Declaration/Clearing
Recommendation
D SDH Multiplexer
D Optional User Selectable LOS Declaration/Clearing
Delay
D Digital Cross Connects
GENERAL DESCRIPTION
The XRT5894 is an optimized four channel 3.3V line
interface unit fabricated using low power CMOS
technology. The device contains four independent E1
channels. Each channel performs the driver and receiver
functions necessary to convert bipolar signals to logical
levels and vice versa. The device requires transformers
on both receiver and transmitter sides, and supports both
balanced and unbalanced interfaces.
The device offers two distinct modes of LOS detection.
The first method, which does not require an external
clock, provides an LOS output indication signal with
thresholds and delay that comply with the ITU G.775
requirements. In the second mode, the user provides an
external clock that increases the delay for LOS
declaration and clearing. This feature provides the user
with the flexibility to implement LOS specifications that
require a delay greater than the G.775 requirements.
ORDERING INFORMATION
Part No.
Operating
Package
64 Lead TQFP (10 x 10 x 1.4mm)
Temperature Range
XRT5894IV
-40°C to +85°C
Rev. 1.10
E2000
EXAR Corporation, 48720 Kato Road, Fremont, CA 94538 z (510) 668-7000 z FAX (510) 668-7017
XRT5894
BLOCK DIAGRAM
Transceiver 1
Transceiver 2
Transceiver 3
Tranceiver 4
RTIP4 (43)
RXPOS4 (47)
1:2
R1
R2
Signal
Peak
Detector
Receive
Comparators
RXNEG4 (46)
TIP
RX Input
RING
RRING4 (42)
V
CC
1
Mux
LOS4 (48)
LOS
Detect
Loss
Delay
O
LOSCNT (45)
LOSSEL (25)
Counter
Transmit
Duty
Cycle
Adjust
TXCLK4 (51)
Line
Drivers
TXPOS4 (49)
TXNEG4 (50)
TTIP4 (53)
R3
0
0
NRZ
To
RZ
2:1
TIP
9.1
Pulse
Shaping
TX OUTPUT
RING
Mux
TRING4 (55)
R4
9.1
1
1
Figure 1. XRT5894 Block Diagram
Receiver Notes
D The same type 1:2CT ratio transformer may be
D LOSCNT (pin 45) is unconnected when LOSSEL is
logic 1, or connected to an external clock when
LOSSEL is logic 0.
used at the receiver input and transmitter output.
D R1 and R2 are both 150Ω for 75Ω operation, or
240Ω for 120Ω operation.
Transmitter Notes
D Return loss exceeds ITU G.703 specification with
D Return loss exceeds ETSI 300 166 specification
these resistors and a 1:2CT ratio input transformer.
with a 1:2 ratio transformer.
LOS (Loss of Signal) Notes
D R3 and R4 are always 9.1Ω for both 75Ω and 120Ω
applications.
D LOSSEL (pin 25) is connected to logic “1” for ITU
G.775 compliant LOS delay, or to logic 0 for user
programmable additional delay.
Rev. 1.10
2
XRT5894
PIN CONFIGURATION
48
33
32
49
TXPOS4
TXCLK3
TXNEG3
TXPOS3
LOS3
TXNEG4
TXCLK4
GND
TTIP4
RXPOS3
RXNEG3
GND
V
CC
TRING4
GND
LOSSEL
NC
GND
TRING1
V
CC
V
CC
RXNEG2
TTIP1
GND
RXPOS2
LOS2
TXPOS2
TXNEG2
TXCLK2
TXCLK1
TXNEG1
TXPOS1
64
17
1
16
64 LEAD THIN QUAD FLAT PACK
(10 x 10 x 1.4 mm, TQFP)
Rev. 1.10
3
XRT5894
PIN DESCRIPTION
Pin #
1
Symbol
LOS1
Type
O
Des cription
Receiver 1 Los s of Signal. Asserted during LOS condition.
Receiver 1 Pos itive Data Out. Positive RZ data output for channel 1.
Receiver 1 Negative Data Out. Negative RZ data output for channel 1.
Pos itive Supply (+3.3V or +5.0V + 5%). Digital circuitry.
Receiver 1 Pos itive Bipolar Input.
2
RXPOS1
RXNEG1
VCC
O
3
O
4
5
RTIP1
I
I
6
RRING1
VCC
Receiver 1 Negative Bipolar Input.
7
Pos itive Supply (+3.3V or +5.0V + 5%). Analog circuitry.
Analog Ground.
8
GND
9
VCC
Pos itive Supply. (+3.3V or +5.0V + 5%). Analog circuitry.
Analog Ground.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
GND
TRING2
VCC
O
O
Trans mitter 2 Negative Bipolar Output.
Pos itive Supply (+3.3V or +5.0V + 5%). Transmitter channel 2.
Trans mitter 2 Pos itive Bipolar Output.
TTIP2
GND
Analog Ground. Transmitter channel 2.
RTIP2
I
I
Receiver 2 Pos itive Bipolar Input.
RRING2
TXCLK2
TXNEG2
TXPOS2
LOS2
Receiver 2 Negative Bipolar Input.
I
Trans mitter 2 Clock Input. Use for clocked mode with NRZ data.1
Trans mitter 2 Negative Data Input. Negative NRZ or RZ data input.1
Trans mitter 2 Pos itive Data Input. Positive NRZ or RZ data input.1
Receiver 2 Los s of Signal. Asserted during LOS condition.
Receiver 2 Pos itive Data Out. Positive RZ data output for channel 2.
Receiver 2 Negative Data Out. Negative RZ data output for channel 2.
Pos itive Supply (+3.3V or +5.0V + 5%). Digital circuitry.
No Connect.
I
I
O
O
O
RXPOS2
RXNEG2
VCC
NC
LOSSEL
GND
I
Los s of Signal Delay Select. “Hi” selects G.775, “Lo” selects user programmable.1
Digital Ground.
RXNEG3
RXPOS3
LOS3
O
O
O
I
Receiver 3 Negative Data Out. Negative RZ data output for channel 3.
Receiver 3 Pos itive Data Out. Positive RZ data output for channel 3.
Receiver 3 Los s of Signal. Asserted during LOS condition.
Trans mitter 3 Pos itive Data Input. Positive NRZ or RZ data input.1
Trans mitter 3 Negative Data Input. Negative NRZ or RZ data input.1
Trans mitter 3 Clock Input. Use for clocked mode with NRZ data.1
Receiver 3 Negative Bipolar Input.
TXPOS3
TXNEG3
TXCLK3
RRING3
RTIP3
I
I
I
I
Receiver 3 Pos itive Bipolar Input.
Note:
1
Has internal pull-up 50KΩ resistor.
Rev. 1.10
4
XRT5894
PIN DESCRIPTION (CONT’D)
Pin #
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
Symbol
GND
Type
Des cription
Analog Ground.
TTIP3
O
Trans mitter 3 Pos itive Bipolar Output.
Pos itive Supply (+3.3V or +5.0V + 5%). Transmitter channel 3.
Trans mitter 3 Negative Bipolar Output.
Analog Ground. Transmitter channel 3.
Pos itive Supply (+3.3V or +5.0V + 5%). Analog circuitry.
Analog Ground.
VCC
TRING3
GND
O
VCC
GND
RRING4
RTIP4
GND
I
I
Receiver 4 Negative Bipolar Input.
Receiver 4 Pos itive Bipolar Input.
Analog Ground.
LOSCNT
RXNEG4
RXPOS4
LOS4
I
O
O
O
I
Los s of Signal Timing Clock Input. For user--programmable LOS delay.1
Receiver 4 Negative Data Out. Negative RZ data output for channel 4.
Receiver 4 Pos itive Data Out. Positive RZ data output for channel 4.
Receiver 4 Los s of Signal. Asserted during LOS condition.
Trans mitter 4 Pos itive Data Input. Positive NRZ or RZ data input.1
Trans mitter 4 Negative Data Input. Negative NRZ or RZ data input.1
Trans mitter 4 Clock Input. Use for clocked mode with NRZ data.1
Analog Ground. Transmitter channel 4.
TXPOS4
TXNEG4
TXCLK4
GND
I
I
TTIP4
O
O
Trans mitter 4 Pos itive Bipolar Output.
VCC
Pos itive Supply (+3.3V or +5.0V + 5%). Transmitter channel 4.
Trans mitter 4 Negative Bipolar Output.
TRING4
GND
Digital Ground.
GND
Analog Ground.
TRING1
VCC
O
O
Trans mitter 1 Negative Bipolar Output.
Pos itive Supply (+3.3V or +5.0V + 5%). Transmitter channel 1.
Trans mitter 1 Pos itive Bipolar Output.
TTIP1
GND
Analog Ground. Transmitter channel 1.
TXCLK1
TXNEG1
TXPOS1
I
I
I
Trans mitter 1 Clock Input. Use for clocked mode with NRZ data.1
Trans mitter 1 Negative Data Input. Negative NRZ or RZ data input.1
Trans mitter 1 Pos itive Data Input. Positive NRZ or RZ data input.1
Note:
1
Has internal pull-up 50KΩ resistor.
Rev. 1.10
5
XRT5894
ELECTRICAL CHARACTERISTICS
Tes t Conditions : V = 3.3V or 5.0V + 5%, T = -40 to 25 to 85°C, Unles s Otherwis e Specified
CC
A
Symbol
Parameter
Min.
Typ.
Max.
Unit
Conditions
DC Electrical Characteris tics
Parameters
VCC
VCC
Voltage Supply
Voltage Supply
3.135
4.75
3.3
5.0
3.465
5.25
V
V
3.3V Operation
5V Operation
Inputs
VIH
VIL
Input High Level
Input Low Level
2.0
2.4
0
5.0
0.8
V
V
Outputs
VOH
Output High Level
Output Low Level
V
V
IOH = -4mA
IOL = 4mA
VOL
0.4
12
Receiver Specifications
RXCL
Allowable Cable Loss
10
dB
Cable loss at 1.024MHz (Relative
to 0dB = 2.37Vp measured from
RTIP or RRING to ground).
RXIM
RXXI
Interference Margin
-15
-12
50
dB
%
With 6dB cable loss
Receiver Slicing Threshold
45
55
% of peak input voltage at -3dB
cable loss
RXLOSSET LOS Must Be Set If RX Sig.
Atten. ² 32dB (For Any Valid
Data Pattern)
15
12
32
dB
dB
Relative to 0dB = 2.37Vp
Measured from RTIP or RRING to
ground.
RXLOSCLR LOS Must Be Cleared If RX Sig.
Atten. < 9dB
9
Relative to 0dB = 2.37Vp
measured from RTIP or RRING to
ground.
RXLOSHYST Hysteresis on Input Data
1
5
dB
For LOS output state change
RXIN
Input Impedance
kΩ
Up to 3.072MHz (Measured from
RTIP or RRING to ground).
Power Specifications VCC = 3.3V
PD
Power Dissipation
460
590
mW
All 1’s Transmit and Receive 75Ω
PD
PC
PC
Power Dissipation
117
770
555
155
900
675
mW
mW
mW
All Drivers Power Down
Power Consumption 75Ω
Power Consumption 75Ω
All 1’s Transmit and Receive
50% data density, Transmit and Re-
ceive
PC
PC
Power Consumption 120Ω
Power Consumption 120Ω
635
475
780
605
mW
mW
All 1’s Transmit and Receive
50% data density, Transmit and Re-
ceive
Power Specifications VCC = 5.0V
PD
PD
PC
Power Dissipation
945
235
1240
290
mW
mW
mW
All 1’s Transmit and Receive 75Ω
All Drivers Power Down
Power Dissipation
Power Consumption 75Ω
1250
1555
All 1’s Transmit and Receive
Note:
Bold face parameters are covered by production test and guaranteed over operating temperature range.
Rev. 1.10
6
XRT5894
ELECTRICAL CHARACTERISTICS (CONT’D)
Tes t Conditions : V = 3.3V or 5.0V + 5%, T = -40 to 25 to 85°C, Unles s Otherwis e Specified
CC
A
Symbol
Parameter
Min.
Typ.
Max.
Unit
Conditions
Power Specifications VCC =5.0V (Cont’d)
PC
PC
Power Consumption 120Ω
Power Consumption 75Ω
1075
1025
1345
1300
mW
mW
All 1’s Transmit and Receive
50% data density, Transmit and Re-
ceive
PC
Power Consumption 120Ω
940
1220
mW
50% data density, Transmit and Re-
ceive
AC Electrical Characteris tics
VTXOUT Output Pulse Amplitude
2.13
2.70
224
2.37
3.0
2.60
3.30
264
V
V
Trans. = 1:2 ratio, 9.1Ω in series
with each end of primary
(RL = 75Ω)
VTXOUT
Output Pulse Amplitude
(RL = 120Ω)
Trans. = 1:2 ratio, 9.1Ω in series
with each end of primary
TXPW
PNIMP
T1
Output Pulse Width
244
5
ns
%
ns
%
ns
Pos/Neg Pulse Unbalanced
TXCLK Clock Period (E1)
TXCLK Duty Cycle
488
50
T2
30
75
70
TSU
Data Set-up Time, TDATA to
TXCLK
50% TXCLK Duty Cycle
50% TXCLK Duty Cycle
THO
Data Hold Time, TDATA to
TXCLK
30
ns
TR
TF
TXCLK Rise Time (10% to 90%)
TXCLK Fall Time (10% to 90%)
40
40
35
ns
ns
ns
T3-noclk
Data Prop. Delay No-Clock
Mode
50
T3-clk
T4
Data Prop. Delay Clock Mode
Receive Data High
470
244
ns
ns
ns
ns
ns
50% TXCLK Duty Cycle
0dB Cable Loss
15pF Load
219
269
40
T5
RX Data Prop. Delay
Receive Rise Time
T6
40
15pF Load
T7
Receive Rise Time
40
15pF Load
Note:
Bold face parameters are covered by production test and guaranteed over operating temperature range.
ABSOLUTE MAXIMUM RATINGS
Storage Temperature . . . . . . . . . . . . -65°C to +150°C
Operating Temperature . . . . . . . . . . -40°C to +85°C
Supply Voltage . . . . . . . . . . . . . . . . . . . -0.3V to +6.0V
ESD Protection . . . . . . . . . . . . . . . . . . >1000V (HBM)
Rev. 1.10
7
XRT5894
Dis abling Output Drivers
Output drivers may be individually disabled (hi-z output) by either of the following methods.
1. Either connect the transmit data inputs TXPOS
and TXNEG for the channel to be disabled to a log-
ic 1 source (VCC), or allow them to float (inputs
have internal pull--up resistors).
2. Connect TXCLK for the channel to be disabled to
logic 0 source (Ground), and also apply data to the
TXPOS and TXNEG inputs of that channel.
TRANSFORMER REQUIREMENTS
Turns Ratio
Line Impedance
Turns Ratio
Line Impedance
1:2 CT
75Ω or 120Ω
1:2
75Ω or 120Ω
Table 1. Input Trans former Requirements
Table 2. Output Trans former Requirements
Note:
The same type 1:2 CT ratio device may be used at both receiver input and transmitter output.
The following transformers have been tested with the
XRT5894:
HALO type TG26-1205(package contains two 1 CT:2 CT ratio transformers)
Pulse type PE-65535 (1:2 CT ratio)
Transpower Technologies type TTI 7154-R (1:2 CT ratio)
Magnetic Supplier Information:
HALO Electronics, Inc.
P.O. Box 5826
Redwood City, CA 94063
Tel. (415) 568-5800
Fax. (415)568-6161
Pulse
Telecom Product Group
P.O. Box 12235
San Diego, CA 92112
Tel. (619) 674-8100
Fax. (619) 674-8262
Transpower Technologies, Inc.
24 Highway 28, Suite 202
Crystal Bay, NV 89402--0187
Tel. (702) 831--0140
Fax. (702) 831--3521
Rev. 1.10
8
XRT5894
TSU THO
TXPOS (n)
TSU THO
TXNEG (n)
TXCLK (n)
TXOUT (n)
T1
T2
TR
TF
TXPW
T3
T3
VTXOUT
VTXOUT
TXPW
Figure 2. Trans mit Timing Diagram
RXIN (n)
T5
T4
T6
T7
RPOS (n)
T5
T6
T7
T4
RXNEG (n)
Figure 3. Receive Timing Diagram
Rev. 1.10
9
XRT5894
RETURN LOSS SPECIFICATIONS
The following transmitter and receiver return loss specifications are based on a typical 1:2CT ratio transformer.
75Ω
120Ω
Frequency Range
51kHz to 102kHz
Min.
16
Typ.
22
Min.
10
Typ.
15
Unit
dB
102kHz to 2.048MHz
2.048MHz to 3.072MHz
16
22
10
15
dB
11
18
10
14
dB
Table 3. Transmitter Return Loss Specification
Transmit Return Loss Notes
D Output transformer ratio is 1:2 (return loss exceeds
D For both 75Ω and 120Ω applications, 9.1Ω, 1% re-
sistors are connected between each end of the
transformer primary and the XRT5894 TTIP and
TRING pins.
ETSI 300 166 with this transformer).
75Ω
120Ω
Frequency Range
51kHz to 102kHz
Min.
16
Typ.
28
Min.
15
Typ.
18
Unit
dB
102kHz to 2.048MHz
2.048MHz to 3.072MHz
22
34
22
25
dB
18
26
20
30
dB
Table 4. Receiver Return Loss Specification
Receiver Return Loss Notes
D Input transformer ratio is 1:2 CT.
D Each half of transformer secondary is terminated
with 150Ω for 75Ω operation, or 240Ω for 120Ω op-
eration (resistors are 1% tolerance).
D Transformer center tap is grounded.
Rev. 1.10
10
XRT5894
SYSTEM DESCRIPTION
This device is a four channel E1 transceiver that provides
an electrical interface for 2.048Mbps applications. Its
unique architecture includes four receiver circuits that
convert ITU G.703 compliant bipolar signals to TTL
compatible logic levels. Each receiver includes a LOS
(Loss of Signal) detection circuit that may be configured
for either a fixed or a user-programmable LOS response
time delay. Similarly, in the transmit direction, four
transmitters convert TTL compatible logic levels to G.703
compatible bipolar signals. Each transmitter may be
operated either with RZ, or NRZ data types. In NRZ mode
a transmit clock is required as well. The following
description applies to any of the four receivers or
transmitters contained in the XRT5894. Therefore, the
suffix numbers for a particular channel are deleted for
simplicity. i.e. “RTIP” applies to RTIP1 through RTIP4.
specified in the ITU G.775. This is done by providing a
user-supplied clock to LOSCNT (pin 45). The “user
programmable mode” is provisioned to allow systems
designers to comply with older versions of LOS
specifications in legacy systems. It needs to be stressed
that the delay for declaration and clearing of the LOS
condition will never be less than the range specified in the
G.775 specification (10-255 pulse intervals).
The LOS detection/clearing circuitry of the XRT5894 in
“automatic” mode will detect LOS when the incoming
signal has “no transitions” i.e. when the signal level is less
than or equal to a signal level A dB below nominal signal
D
level, for N consecutive pulse intervals, where 10<N<255.
The value of A
can vary between 10dB to 32dB
D
depending on the ones density of the incoming signal
assuming the received data has minimum permissible
ones density. Furthermore LOS detect is cleared when
the incoming signal has “transitions,” i.e. when the signal
Receiver Operation
level is greater than or equal to a signal level of A dB
below nominal, for N consecutive pulse intervals, where
C
A bipolar signal is transformer-coupled to the receiver
differential inputs (RTIP and RRING). The receiver is able
to tolerate up to 12dB of line loss measured at 1.024MHz.
It contains slicing circuitry that automatically samples the
incoming data at a fixed percentage (50% nominal) of the
peak signal amplitude. A precision peak detector
maintains the slicing level accuracy. The TTL compatible
receiver output data rails appear at the RXPOS and
RXNEG pins. The pulse width of this data; which is in RZ
format, is a function of the amount of the cable loss
present.
10<N<255. The value of A can vary between 9dB to
C
31dB depending on the ones density of the incoming
signal assuming the received data has minimum
permissible ones density. Each pulse interval is 488ns at
E1 rates. The absolute value of A is always smaller than
C
A by at least 1dB.
D
The LOS detection/clearing criteria described above is
fully compliant with G.775 LOS specification. In the “user
programmable” mode the user has the option of
extending the declaration and clearing delay (10<N<255)
by an amount which is equal to 2048 x T. T is the time
period of the clock supplied to LOSCNT (pin 45) by the
user.
Receiver Los s Of Signal Detection (LOS)
Absence of signal at any receiver input is detected by the
loss of signal (LOS) circuit. One LOS detection circuitry is
provisioned for each receiver. The LOS signal is asserted
(LOS=1) when a LOS condition is detected and is cleared
(LOS=0) when a valid input signal is restored.
Nominal signal level is defined as 2.37V peak measured
between RTIP or RRING and ground. (This voltage will
be present in 75Ω applications using a 1:2 CT ratio input
transformer terminated in 300Ω with the center tap
grounded with 0dB of cable and a 2.37V peak amplitude
transmit pulse at the cable input.)
Two modes of LOS circuit operation are supported.
These distinct modes are called “automatic” and
“user-programmable”. When LOSSEL (pin 25) is set to
logic “1”, the automatic mode is selected. In this mode the
LOS condition will be declared and cleared in full
compliance with ITU G.775 specification. When LOSSEL
is connected to logic “0”, the user-programmable delay
mode is enabled. In this mode the user has the option of
extending the delay of LOS declaration and clearing
Trans mitters
This device contains four identical ITU G.703 compliant
transmitters. The output stage of each transmitter is a
differential voltage driver. External resistors need to be
connected to the primary of output transformer. This is
necessary to maintain an accurate source impedance
Rev. 1.10
11
XRT5894
that ensures compliance to ETSI 300 166 return loss
requirement.
present at this pin, the transmitter detects its presence
and operates in the clocked mode. In this mode, the
transmit input should be supplied with full-width NRZ
pulses. If a clock is not present at the TXCLK input (pin is
left open), the part operates in the clockless mode. In this
mode, RZ data should be supplied to the device. Each
transmit channel of XRT5894 has a duty cycle correction
circuitry. This enables the device to produce output
bipolar pulses fully compliant with G.703 despite having
TXCLK signal with 30% to 70% duty cycle.
TTL compatible dual rail transmit data signals are
supplied to TXPOS and TXNEG inputs. The transmitter
differential outputs TTIP and TRING are connected to the
output transformer primary through series 9.1Ω resistors.
All the four transmitters can be operated in two distinct
modes of operation referred to as “clocked” or “clockless”
modes. The operational mode is selected automatically
based on the signal provided to TXCLK input. If a clock is
269 ns
(244 + 25)
Nominal pulse
20%
10%
V = 100%
194 ns
(244 -- 50)
10%
20%
50%
244 ns
219 ns
(244 -- 25)
10%
0%
10%
10%
10%
20%
488 ns
(244 + 244)
Note: V corresponds to the nominal peak value
Figure 4. CCITT G.703 Puls e Template
Rev. 1.10
12
XRT5894
Trans mitter Output Puls e Meas urement
Figure 5 shows a typical transmit pulse plotted on the template shown in ITU G.703 Figure 15/G.703. The following
conditions apply:
V
CC
=3.30V
Transmitter output transformer secondary terminated with 120Ω
All ones signal
Receiver output looped backed into transmitter digital input
Operation without transmitter clock (RZ data)
Measurement made with a Tektronix TDS640 digital scope set to full bandwidth
1.2
1.0
0.8
0.6
0.4
0.2
0
-0.2
-244
-122
0
122
244
Time (ns )
Figure 5. XRT5894 Output Puls e
Rev. 1.10
13
XRT5894
Transmitter Output Return Loss Measurements
The following measurements were made with a Wandel
and Goltermann SNA--2 Network Analyzer equipped with
an RFZ--1 75Ω Return Loss Bridge. A 75Ω to 120Ω
impedance matching transformer was used to make the
120Ω measurement. A network analyzer calibration run
subtracted out the effects of this transformer.
This configuration was used for both 75Ω and 120Ω
measurements. The only change was the termination
resistance provided by the return loss bridge.
Test Results:
Table 5 compares measured output return loss with
requirements in ETSI FINAL DRAFT prETS 300 166,
June1993. These resultsshow that measuredreturnloss
is mainly determined by the characteristics of the output
transformer. This is particularly evident for the 120Ω load
where the measured result is better than the calculated
value.
Test Conditions:
D Output transformer ratio was 1:2.
D Transmitter series resistors (R3 and R4 in Figure 1)
were 9.1Ω .
D Device was powered from a 3.3V source, transmitter
was enabled, and no output data was present.
Specified
Frequency
Frequency
(KHz)
ETSI Spec.
(Min. dB)
Meas. Value (dB)
Meas. Value (dB)
75Ω Load
120Ω Load
0.025 fb
0.05 fb
1.5 fb
51.2
102.4
3072
6
8
8
22.6
22.6
18.0
15.4
15.7
14.6
Table 5. Transmitter Output Return Loss Measurements
Notes:
fb = 2048KHz
This data shows that the XRT5894 is fully compliant with the ETSI Output Return Loss Specification for E1 operation with either
75Ω or 120Ω loads.
Rev. 1.10
14
XRT5894
The following pictures show typical results of measurements that made over a 50 KHz to 3.5MHz frequency range.
Figure 6. 75Ω Return Los s Meas urement
Figure 6 shows a return loss better than 20dB at low frequencies that decreases to about 12dB at 3.5MHz. Since the
source and load resistances are well--matched, the return loss degradation is due to the transformer.
Figure 7. 120Ω Return Los s Meas urement
Figure 7 shows that for the 120Ω case, transformer characteristics improve return loss at lower frequencies. At 3.5 MHz,
return loss is close to the calculated 13.8dB for a 75Ω source terminated with 120Ω.
Rev. 1.10
15
XRT5894
Output Trans former Selection
A 1:2 ratio transformer is recommended for both 75Ω and 120Ω operation because the transmitter, when equipped with
this device, meets both the ITU G.703 output pulse amplitude requirement and, the ETSI return loss specification.
Although a center--tapped output transformer is not required, choosing a part with a center-tapped secondary allows the
use of the same type of unit at the receiver input.
A theoretical justification for the 1:2 ratio transformer follows:
RS
TTIP
R3
pos
1:n
VS
VS
pos
neg
V
O
R
L
TRING
RS
R4
neg
Figure 8. Trans mitter Line Driver Model
Where:
Vs
Rs
= Vs
= Rs
= 1.25V typical (Differential line driver peak output voltage swing)
pos
pos
neg
= 0.8Ω typical (Differential line driver internal source resistance)
neg
R3 = R4 = 9.1Ω (Differential line driver external source resistance from Figure 1)
R = 75Ω or 120Ω (Transmitter load resistance)
L
n = 2 (Transformer turns ratio)
Vo = Transmitter peak output voltage (Measured across R = 75Ω or R = 120Ω )
L
L
Figure 9 may be converted to a single--ended model:
RS
RS
ext
int
1:n
V
S
V
O
R
L
Figure 9. Single-ended Line Driver Model
Where:
VS = Vs + Vs
pos
neg
neg
RS = RS
+ Rs
pos
int
RS = R3 + R4
ext
Rev. 1.10
16
XRT5894
This may be further simplified:
R
I
T
V
s
V
eq
Figure 10. Equivalent Circuit
Where:
R = RS + Rs
T
int
ext
R
n2
L
R
=
eq
Therefore:
Vs
I =
R
+ Req
T
V
eq
= I R
eq
V = n V
o
eq
And:
R + R
T
eq
Return Loss = 20 log
R -- R
T
eq
Table 5 contains the results of calculations made with these equations. The numbers show that output pulse amplitude
is within millivolts of the nominal values of 2.37V and 3.00V specified by ITU G.703 for 75Ω and 120Ω operation. Also,
the 1:2 ratio transformer provides an almost-perfect match for 75Ω operation, and return loss is well within the ETSI
specification for the 120Ω load.
Load Res is tance
Puls e Amplitude
Vo (Volts Peak)
Output
Return Los s (dB)
RL (Ω)
75
2.43
3.01
31.3
13.8
120
Table 5. Calculated Trans mitter Puls e Amplitude and Return Los s
Rev. 1.10
17
XRT5894
64 LEAD THIN QUAD FLAT PACK
(10 x 10 x 1.4 mm, TQFP)
Rev. 2.00
D
48
33
49
32
D
64
17
1
16
B
A
2
C
A
α
Seating Plane
A
1
L
INCHES
MILLIMETERS
SYMBOL
MIN
MAX
MIN
MAX
A
0.055
0.002
0.053
0.005
0.004
0.465
0.390
0.063
0.006
0.057
0.009
0.008
0.480
0.398
1.40
0.05
1.35
0.13
0.09
11.80
9.90
1.60
0.15
A
1
A
2
1.45
B
C
D
D
e
0.23
0.20
12.20
10.10
0.50 BSC
0.75
1
0.020 BSC
L
0.018
0°
0.030
0.45
α
7°
0°
7°
Note: The control dimension is the millimeter column
Rev. 1.10
18
XRT5894
NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to im-
prove design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits de-
scribed herein, conveys no license under any patent or other right, and makes no representation that the circuits are
free of patent infringement. Charts and schedules contained herein are only for illustration purposes and may vary
depending upon a user’s specific application. While the information in this publication has been carefully checked;
no responsibility, however, is assumed for inaccuracies.
EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or
malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly
affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation
receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the
user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circum-
stances.
Copyright 2000 EXAR Corporation
Datasheet March 2000
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
Rev. 1.10
19
相关型号：
XRT5997IV-F
PCM Transceiver, 1-Func, CEPT PCM-30/E-1, CMOS, PQFP100, 14 X 14 MM, 1.40 MM HEIGHT, GREEN, TQFP-100
EXAR
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