English

BL1920
2.5Gbps Low Noise CMOS Optical
Trans-Impedance Amplifier
General Description
The BL1920 is a low noise low power smart CMOS optical trans-impedance amplifier with single input and differential
output. Received power monitoring and automatic gain control (AGC) are integrated. It is suitable for 2.5Gbps data rate
operation with a high trans-impedance gain up to 87db to ensure good sensitivity.
The BL1920 offers an internal regulator to bias the PIN photodiode, while for APD photodiode ROSA an external bias
circuit is needed.
A replica of the average photodiode current is available at the IMON pad for photo alignment and received power
monitoring (SFF-8472 compliant).
For optimum system performance, the BL1920 die should be mounted with a GaAs or InGaAs PIN photo-detector
inside a focused TO-CAN or other optical sub-assembly.
Features

195nARMS input referred noise at 2.1G bandwidth

Standard CMOS process

Typical 24kΩ differential trans-impedance

Monitor output (SFF-8472 compliant)

AGC provides dynamic range of 37dB


Differential CML output
Internal or external bias for photodiode (PIN
photodiode, APD photodiode)

Standard 3.3V supply

Available in die form only
Application Fields
2x Fiber Channel, EPON, GPON, PCI Express, ATM/SONET
Block Diagram
IMON
Regulator
PINC
Regulator
DC
restore
Low
pass
filter
Phase
splitter
PINA
Low
pass
filter
VDD_TIA
V1.0
Output
buffer
OUTP
OUTN
Swing
detector
AGC
CEC – Shanghai Belling Co. Ltd.
1
BL1920
Ordering Information
Part number
Package
Operating temperature
BL1920
Wafer
-40℃ to 85℃
Revision History
V1.0
Revision
Level
Date
Description
A
Preliminary
August 2014
Internal Release
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2
BL1920
TABLE OF CONTENTS
GENERAL DESCRIPTION .................................................................... 1
FEATURES.............................................................................................................................................................1
APPLICATION FIELDS ............................................................................................................................................1
BLOCK DIAGRAM .................................................................................................................................................1
ORDERING INFORMATION ................................................................. 2
REVISION HISTORY ............................................................................. 2
1.0 PRODUCT SPECIFICATION ............................................................ 4
1.1 ABSOLUTE MAXIMUM RATINGS.............................................................................................. 4
1.2 RECOMMENDED OPERATING CONDITIONS .............................................................................. 4
1.3 DC CHARACTERISTICS .......................................................................................................... 4
1.4 AC CHARACTERISTICS .......................................................................................................... 5
1.5 DYNAMIC CHARACTERISTICS ................................................................................................. 5
1.6 PAD INFORMATION ............................................................................................................... 6
2.0 APPLICATION INFORMATION ........................................................ 8
2.1 FUNCTIONAL DESCRIPTION .................................................................................................... 8
2.1.1 Main Trans-Impedance Amplifier (TIA) ............................................................................................ 8
2.1.2 Phase Splitter ....................................................................................................................................... 8
2.1.3 Automatic Gain Control (AGC).......................................................................................................... 8
2.1.4 Output Buffer........................................................................................................................................ 8
2.1.5 Received Power Monitor .................................................................................................................... 8
2.2 RECOMMENDED CONNECTION ................................................................................................ 9
2.2.1 Selecting the Monitor Resistor.......................................................................................................... 9
2.2.2 Treatment of PINC ............................................................................................................................... 9
2.3 TO-CAN LAYOUT .................................................................................................................. 9
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BL1920
1.0 Product Specification
1.1 Absolute Maximum Ratings
Device can fail or be damaged by operating beyond these limits.
Table 1-1
Absolute Maximum Ratings
Symbol
Parameter
Rating
Units
VCC
Supply Voltage (VCC-GND)
-0.4 to 4
V
Tsto
Storage Temperature
-65 to 150
℃
Tjun
Junction temperature
-40 to 125
℃
Iin
PINA input current
0 to 3
mApp
VPINA
Input voltage at PINA
-0.4 to 2
V
IPINC
Maximum average current sourced out of PINC
6
mA
VPINC, VMON
Input voltage at PINC and IMON (1kOhm load)
-0.4 to VCC+0.4
V
VOUT
Maximum output voltage at OUTP and OUTN
0 to VCC
V
HBM MODE ESD
2
KV
(1)
ESD
Note:
1: PINA has no ESD protection and thus, make sure that ESD voltage at pin PINA never exceeds 500V.
1.2 Recommended Operating Conditions
Table 1-2.
Recommended Operating Conditions
Symbol
Parameter
Rating
Units
VCC
Supply Voltage (VCC-GND)
3.3 ± 10%
V
CPD
Max. photodiode capacitance
0.5
pF
TA
Operating ambient temperature
-40 to 85
℃
1.3 DC Characteristics
All parameters are characterized under recommended operating condition. Typical specifications are for VCC = 3.3V,
TA = 27°C, CPD = 0.3pF, unless otherwise noted.
Table 1-3.
DC Characteristics
Symbol
Parameter
VPINC
Internal regulator output voltage for PIN
photodiode cathode bias internally
2.5
V
VPINA
Photodiode anode bias voltage
0.8
V
ICC
Supply current
V1.0
Min
28
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Typ
34
Max
41
Units
mA
4
BL1920
Rout(diff)
Differential output resistor
Ω
100
1.4 AC Characteristics
All parameters are characterized under recommended operating condition. Typical specifications are for VCC = 3.3V,
TA = 27°C, CPD = 0.3pF, unless otherwise noted.
Table 1-4
AC Characteristics
Symbol
Parameter
Condition
Min.
Typ.
Max.
LFC
Low frequency cutoff
AGC non lick-in
35
KHz
Voutp_p
Peak to peak
differential output
voltage
100Ω differential load
320
mV
DCD
Duty cycle distortion
2.125Gbps
50
2.5Gbps
60
ps
7
Deterministic Jitter
( include DCD )
DJ
PDJ
In_rms
2.125Gbps, 2 – 1 PRBS
60
23
70
ps
2.5Gbps, 2
2.125Gbps, 2 – 1 PRBS
29
23
34
ps
2.5Gbps, 2
Minimum input optical
(2)
sensitivity
Imon_off
Monitor output offset
Imon_erro
r
Monitor output
accuracy
– 1 PRBS
100k to 2.1GHz, Cin =
0.5pf
(1)
PIN_mean
_min
– 1 PRBS
7
Pattern dependant
jitter (at crossing point)
without DCD
Input referred noise
Units
2.5Gbps, BER < 10
-10
195
nA
-27.7
dBm
VMON = 0 to 2V
2
uA
±1. 5
dB
Note:
1. 2.1GHz bandwidth Bessel LPF at the output terminal and 0.5pF capacitance at input.
2. At stated data rate and BER. Responsivity = 0.9 A/W, Extinction Ratio = 10, suppose PD capacitance = 0.5pF
1.5 Dynamic Characteristics
All parameters are characterized under recommended operating condition. Typical specifications are for VCC = 3.3V,
TA = 27°C, CPD = 0.3pF, unless otherwise noted.
Table 1-5
Symbol
Parameter
G
Trans-impedance (differential)
BW
-3dB bandwidth, Cin = 0.3pF
τ
AGC
IAGC
V1.0
Dynamic Characteristics
Min
Typ
Max
KΩ
24
1.62
1.94
Units
2.23
GHz
AGC loop time constant
15
us
AGC threshold
40
uApp
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BL1920
IOVL
Input overload current
3
mApp
Power supply rejection
1MegHz<f<30MegHz
30
dB
Power supply rejection, f < 1MHz
40
dB
PSRR
1.6 PAD Information
Figure 1-6
BL1920 Pin Assignment
15
14
13
11
12
1
10
2
9
I30V10
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Table 1-6
4
5
6
7
8
BL1920 Pin Definitions
Pin No.
Pin Name
1
PINC
Common PIN input. Connect to photo diode cathode and a 470pF capacitor to GND.
2
PINA
Active PIN input. Connect to photo diode anode.
3
VCC
Positive power supply.
4
IMON
Analog current source output. A replica of average photodiode current.
5
NC
--
6
NC
--
7
NC
--
8
GND
Ground pin.
9
VON
Negative data output pin.
10
VOP
Positive data output pin.
11
GND
Ground pin.
12
AGC
Monitor or force AGC voltage.
V1.0
Description
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BL1920
13
NC
14
VDD_TIA
15
VCC
V1.0
-Internal regulator output voltage for the main TIA power supply.
Positive power supply.
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BL1920
2.0 Application Information
2.1 Functional Description
The BL1920 is a CMOS trans-impedance amplifier with single input and differential output. It consists of a main TIA
block, a phase splitter for single to differential ended signaling, AGC for trans-impedance control, an output buffer, and a
received power monitor. The PINA pin gets the input photodiode current and the OUTP/OUTN pins get the differential
output voltage.
2.1.1 Main Trans-Impedance Amplifier (TIA)
The TIA consists of a high gain single-ended amplifier and a feedback resistor. Virtually all of the input current passes
through the feedback resistor defining the voltage at the output.
An on-chip low dropout regulator is designed for TIA to give excellent noise rejection up to several MHz. Higher
frequency power supply noise is removed by the external decoupling capacitor.
2.1.2 Phase Splitter
The phase splitter is designed to convert the single ended signal into differential ended signal. It consists of a high
speed differential amplifier and a feedback circuit that serves as an active low pass filter (shown in figure 2-1-2). The
whole loop is self-biased and then, a DC value is obtained as the common voltage of outp and outn. Their AC signals
are filtered and the cut-off frequency is about tens of KHz, which makes the output signals keep differential.
Figure 2-1-2 Phase splitter Block Diagram
Opa
Low
pass
filter
outp
Amp
inp
outn
2.1.3 Automatic Gain Control (AGC)
The dynamic range of input current is 10uA-1mA, which requires a changeable trans-impedance to ensure that the TIA
works properly. If the input current is large, the trans-impedance is supposed to be decreased so that the TIA operates
in linear region. A MOS transistor in the triode region is used as a “voltage controlled resistor” to achieve the transimpedance variation. The AGC circuit changes the voltage of the MOS transistor corresponding to the input current.
In the BL1920, the AGC only operates on signals greater than 50uA. When “signal detect” function is set in the following
post amplifier, the knee in the gain response is important. It also aids in active photodiode alignment.
The AGC pad allows the AGC control voltage to be monitored or controlled externally.
2.1.4 Output Buffer
The power supply of the chip is 3.3V, which is not suitable for the phase splitter. So, the output buffer is needed to shift
the output signals of the phase splitter to compliant with 3.3V supply. The output buffer is designed to drive differential
100Ω load with the CML output format.
2.1.5 Received Power Monitor
This block monitors the average photodiode current through a high impedance current source. The output is compatible
with the DDMI Received Power Specification (SFF-8472). Meanwhile, the block also contains a DC restore function in
order that the core TIA works properly. The voltage on the IMON pad is in the range of 0 to 2.5V.
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BL1920
2.2 Recommended connection
When PIN photodiode is used, the anode of the photodiode is connected to the input of the TIA and the cathode is
connected to AC ground, such as PINC terminal with decoupling capacitor. Reverse DC bias is applied to reduce the
photodiode capacitance. Avalanche photodiode can be biased externally to a higher voltage.
Figure 2-2-1. Internal PIN Bias
GND
VCC
VCC(3.3V)
C2=1nF
PINC
OUTP
C1=470P
Limiting
Amplifier
BL1920
PIN
OUTN
IMON
PINA
Rm=1K
Figure 2-2-2. External APD Bias
VCC
Rb=500
GND
VCC(3.3V)
VPD(20-40V)
C2=1nF
PINC
OUTP
Limiting
Amplifier
BL1920
APD
IMON
OUTN
PINA
Rm=1K
2.2.1 Selecting the Monitor Resistor
The monitor output sources a replica average photodiode current for monitoring purpose. An external resistor is
connected to this pad to convert the current to a voltage. The voltage is in the range of 0 to 2.5V, requiring the resistor
value to be set according to the input current. A typical value is set to be 1kOhm.
2.2.2 Treatment of PINC
PINK requires bypassing to ground with a 470 pF capacitor when biasing a photo diode. If PINK is not used to bias the
photo diode, it is not necessary to bypass.
2.3 TO-Can Layout
Ball bonding is recommended with a 1 mil gold wire. For performance reasons the PINA pad is smaller than the others
and also have less via material connected to it. It requires more care in setting of the bonding parameters. For the
same reason PINA has not ESD protection.
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BL1920
Figure 2-3-1
Typical Layout Diagram with Photodiode Mounted on TO-Can
OUTN
LOGO
OUTP
CAP
Photodiode
VCC
IMON
CAP
Figure 2-3-2
BL1920 PAD Coordinates
Coordinates
Pin No.
15
14
13
11
12
1
10
2
9
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Table 2-3-2
V1.0
4
5
6
Name
7
8
X
Y
1
PINC
-398
68
2
PINA
-398
-68
3
VCC
-232
-398
4
IMON
-122
-398
5
NC
-41
-398
6
NC
40
-398
7
NC
121
-398
8
GND
232
-398
9
VON
398
-67
10
VOP
398
67
11
GND
233
398
12
AGC
101
398
13
NC
0
398
14
VDD_TIA
-101
398
15
VCC
-231
398
BL1920 PAD Coordinates
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