10 Gbit/s
AGC Amplifier
GD19902
Preliminary
General Description
The GD19902 device is an amplifier de-
signed for Automatic Gain Control
(AGC), with high input overload, high
gain, intended for use in high bandwidth
applications such as 10 Gbit/s STM-64/
OC-192 receiver front-end.
GD19902 provides on chip peak detect
circuitry as well as monitors on the output
DC levels for balancing the outputs.
Gain is controlled from -3 dB to +20 dB
through the AGC input.
The differential inputs can be used with a
single-ended as well as a true differential
input signal.
GD19902 is DC coupled.
On-chip 50
W
termination of the input and
output signals reduces the need for ex-
ternal components.
Together with a 10 Gbit/s CDR
(GD16544) error free operation is ob-
tained with < 2 × 8 mV
PP
input signal.
Features
l
Gain: 20 dB.
High output: 1.0 V
PP.
Output peak-peak monitor.
Single power supply: -8 V.
No external choke required.
Bandwidth: 8 GHz (-3 dB), typical.
Power dissipation: 2.8 W, typical.
Output DC level monitors.
l
l
l
l
l
l
l
AGC
Pdet
Pdetr
NAGC
Applications
GND
l
VIN
VOUT
l
Tele Communication transmission
systems:
– SDH STM-64
– SONET OC-192
WDM applications.
10 Gbit optical receivers.
VINN
VOUTN
l
VEE
DCout DCoutn
Data Sheet Rev.: 06
Functionality
The typical application diagram for GD19902 is shown in
Figure 1.
Output Swing [mVpp]
1400
1200
1000
800
600
400
200
0
-3V
-2.75V
-2.5V
-2.2V
The GD19902 can be driven with a single ended or a differential
input. In the case of single ended input, the differential output
swing is halved, and the other input port must be AC shorted to
GND. The inputs can be DC coupled, but then the applied cir-
cuit must not alter the quiescent input voltage. The outputs can
be DC coupled, but then the DC level will be reduced from
–1.4 V to –0.7 V.
The amplifier gain is controlled through the pins AGC and
NAGC. These are
not
differential pins. The AGC pin is used for
variable gain, and the NAGC pin for fixed maximum gain (if con-
nected to GND). The two pins must
not
be connected simulta-
neously. If the two pins are both left open, maximum gain is
also achieved, even though this setting is not recommended.
The gain is fixed, when a fixed voltage is applied on the AGC
pin as illustrated in
Figure 2.
The maximum output is clamped to
approximately 1.2 V
PP
.
An external AGC circuit can be applied to the AGC pin as re-
quired in the specific application. The Pdet output varies with re-
spect to the output peak-to-peak swing according to
Figure 3
shown below. The Pdetr output accommodates for variations in
the Pdet output caused by power supply and case temperature
drift. The datasheet for the evaluation board GD99902 includes
schematic for a suggested AGC circuit.
To keep the DC levels of the outputs balanced, the GD19902
features internal DC level monitors for the output pins. An exter-
nal feedback circuit from pin DCout and DCoutn back to one of
the inputs (through a bias T) will balance out any drift in the out-
put DC levels. This feature serves two purposes. Primarily in
the case of DC coupled outputs, the DC levels must be bal-
anced at the input of the following DeMUX circuit (e.g.
GD16544). Secondly, the output buffer transistors should be
kept at a fixed operating point. The datasheet for the evaluation
board GD99902 includes schematic for a suggested DC nulling
circuit.
AGC Loop
-4V
0
50
100
150
200
250
300
Input Swing per Input Leg with Differential Input [mVpp]
Figure 2.
Gain characteristics for fixed gain operation. Typical
-2,20
-2,22
Peak Detect Voltage, Vpdet [V]
-2,24
-2,26
-2,28
-2,30
-2,32
-2,34
-2,36
AGC
Pdet
Pdetr
NAGC
-2,38
-2,40
*: Optional
0
200
400
600
800
1000 1200
Single Ended Output Swing [mVpp]
1400
VIN
VOUT
*
*
Figure 3.
Peak detect output vs. output swing.
-4.0 V < V
AGC
< -2.2 V. Typical
For Single-ended
Operation
VINN
VOUTN
DCout
DCoutn
DC Nulling Loop *
Figure 1.
Application Diagram
Data Sheet Rev.: 06
GD19902
Page 2 of 8
Application
The GD19902 can be used with the GD19906 Transimpedance Amplifier in conjunction with other GIGA products as shown in the
figure below – composing a full 10 Gbit/s receiver front-end.
PIN
diode
GD19906
Transimpedance
Amplifier
1
GD19902
AGC
Amplifier
2
GD16544
CDR/PLL
DeMUX
16 ×
622
Mbit/s
Figure 4.
Building blocks for a 10 Gbit/s reception system.
The GD19906 device converts and pre-amplifies the current from the PIN diode, which is delivered to the AGC amplifier GD19902
single-ended. This device produces a differential signal suitable for driving the GD16544 DeMUX. The 16 demultiplexed data sig-
nals (and clock) available at the DeMUX output can be fed to a system ASIC. If required, a second level demultiplexer (GD16334)
can be added for further reduction of the signal speeds. A set of four synchronized GD16334 demultiplexers will bring the original
10 Gbit/s signal down to 78 Mbit/s.
Please see separate data sheets for the TIA amplifier and the DeMUX devices.
GIGA offers corresponding building blocks for the transmit functions (see GD19901, 19903, and GD16555).
The required optical input power in the set-up shown in Figure 4 can be estimated as follows. The current generated by the PIN
diode is given as Id = Pd / r, and the voltage swing after the TIA as VTIA = Id × RTIA. The GD19902 typically requires 50 mV
PP
at
the input, the GD19906 has a typical transimpedance gain of 500
W,
and assuming a PIN diode responsivity of 1 A/W, we get:
VTIA = 50 mV
Id = VTIA/RTIA = 50 mV / 500
W
= 0.1 mA
Pd = Id × r = 0.1 mA × 1 A/W = 0.1 mW
Assuming an optical non-return-to-zero (NRZ) signal with 50 % duty cycle between one’s and zero’s, this corresponds to an optical
average power of:
Popt = Pd × 50 % = 0.1 mW × 0.5 = 0.5 mW or Popt = 10 × log10(0.05 mW/1 mW) = -13 dBm.
At the output of the GD19902 the each leg of the differential signal will have an amplitude swing of:
Vout = VTIA × G = 50 mV × 10^(20 dB/20) = 500 mV (single-ended) or 1000 mV (differential).
This calculation does not include noise generated at the optical PIN diode nor in the TIA amplifier.
Data Sheet Rev.: 06
GD19902
Page 3 of 8
Pin List
Mnemonic:
VIN, VINN
VOUT, VOUTN
Pdet
Pdetr
AGC
NAGC
GND
Pin No.:
27, 25
59, 61
3
49
16
36
1, 4, 9, 14, 19, 20,
21, 22, 23, 24, 26,
28, 29, 30, 31, 32,
33, 34, 38, 43, 48,
51, 52, 53, 54, 55,
56, 57, 58, 60, 62,
63, 64, 65, 66, 67,
68
17, 18, 35
5, 47
2, 6, 7, 8, 10, 11,
12, 13, 15, 37,
39, 40, 41, 42, 44,
45, 46, 50
Pin Type:
AC
AC
DC
DC
DC
DC
PWR
Description:
Data Input, differential 10 Gbit/s. DC coupled, see
Figure 1.
Data Output, differential 10 Gbit/s. DC coupled, see
Figure 1.
Peak Detect Output.
Peak Detect Reference Level Output.
AGC Control Line Input.
Maximum Gain Input.
Ground.
VEE
DCoutn, DCout
NC
PWR
DC
Negative supply voltage.
Output DC levels.
Not Connected.
Package Pinout
DCoutn
GND
GND
GND
GND
AGC
16
Pdet
VEE
17
NC
NC
NC
NC
NC
NC
NC
NC
NC
15
10
12
13
14
11
1
2
3
4
5
6
7
8
9
VEE
GND
GND
GND
GND
GND
GND
VINN
GND
VIN
GND
GND
GND
GND
GND
GND
GND
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
GND
GND
GND
GND
GND
GND
GND
VOUTN
GND
VOUT
GND
GND
GND
GND
GND
GND
GND
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
Figure 5.
Package 68 pin MLC, Top View
Data Sheet Rev.: 06
GD19902
Page 4 of 8
35
VEE
GND
NC
NC
DCout
Pdetr
NC
NC
GND
GND
NC
NC
NC
NC
GND
NC
NAGC
Maximum Ratings
These are the limits beyond which the component may be damaged.
All voltages in the table are referred to GND.
All currents in the table are defined positive out of the pin.
Symbol:
VEE
VIN,VINN
VOUT, VOUTN
AGC
NAGC
T
0
T
S
Characteristic:
Negative Supply
Input Voltage
Output Voltage
AGC Voltage Level
NAGC Voltage Level
Operating Temperature
Storage Temperature
Case
-4.0
-4.0
0
-65
Conditions:
MIN.:
-9
-2.5
TYP.:
MAX.:
GND
0.5
1.75
0.5
0
70
125
UNIT:
V
V
V
PP
V
V
°C
°C
Precautions
Class 1 ESD
u
Output: 500 V; Input: 100 V
DC Characteristics
T
CASE
= 0 °C to 70 °C, VEE = -8.0 V ±5 %.
All voltages in the table are referred to GND.
All input signal and power currents in the table are defined positive into the pin.
All output signal currents are defined positive out of the pin.
Symbol:
VEE
IEE
P
DISS
V
VIN,VINN
V
VOUT,VOUTN
V
DCout, DCoutn
Characteristic:
Negative Supply
Negative Supply Current
Power Dissipation
Quiescent Input Voltage
Quiescent Output Voltage
Output DC Levels
AC coupled outputs
AC coupled outputs
Conditions:
MIN.:
-8.4
-300
TYP.:
-8.0
-350
2.5
-0.85
-1.4
-1.4
MAX.:
-7.6
-375
3.15
UNIT:
V
mA
W
V
V
V
Data Sheet Rev.: 06
GD19902
Page 5 of 8
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