ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
4.25-Gbps Transimpedance Amplifier With AGC and RSSI
Check for Samples: ONET4291T
FEATURES
APPLICATIONS
•
•
•
•
•
•
•
•
1
•
•
•
2.8-GHz Bandwidth
3.2-kΩ Differential Transimpedance
Automatic Gain Control (AGC)
8.8-pA/√Hz Typical Input Referred Noise
2-mAp-p Maximum Input Current
Received Signal Strength Indication (RSSI)
CML Data Outputs With On-Chip 50-Ω
Back-Termination
On-Chip Supply Filter Capacitor
Single 3.3-V Supply
Die Size: 0,78 × 1,18 mm
•
•
•
SONET/SDH Transmission Systems at OC24
and OC48
4.25-Gbps, 2.125-Gbps, and 1.0625-Gbps
Fiber-Channel Receivers
Gigabit Ethernet Receivers
PIN Preamplifier-Receivers
DESCRIPTION
The ONET4291T is a high-speed transimpedance amplifier used in optical receivers with data rates up to 4.25
Gbps.
It features a low input referred noise, 2.8-GHz bandwidth, automatic gain control (AGC), 3.2-kΩ transimpedance,
and received signal strength indication (RSSI).
The ONET4291T is available in die form and is optimized for use in a TO can.
The ONET4291T requires a single 3.3-V supply, and its power-efficient design typically dissipates less than 56
mW. The device is characterized for operation from –40°C to 85°C ambient temperature.
AVAILABLE OPTIONS
TA
DIE
–40°C to 85°C
ONET4291TY
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2011, Texas Instruments Incorporated
ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
BLOCK DIAGRAM
The ONET4291T is a high-performance, 4.25-Gbps transimpedance amplifier consisting of the signal path,
supply filter, a control block for dc input current cancellation, automatic gain control (AGC), received signal
strength indication (RSSI), and a band-gap voltage reference and bias current generation block.
The signal path comprises a transimpedance amplifier stage, a voltage amplifier, and a CML output buffer.
The on-chip filter circuit provides filtered VCC for the photodiode and for the transimpedance amplifier. The dc
input current cancellation and AGC use internal low-pass filters to cancel the dc current on the input and to
adjust the transimpedance amplifier gain. Furthermore, circuitry to monitor the received signal strength is
provided.
A simplified block diagram of the ONET4291T is shown in Figure 1.
VCC
275 pF
GND
220 W
Band-Gap Voltage
Reference and
Bias Current
Generation
200 pF
FILTER
DC Input Current
Cancellation,
AGC, and RSSI
RSSI
RF
OUT+
IN
OUT–
Transimpedance Amplifier
Voltage Amplifier
CML Output Buffer
B0066-01
Figure 1. Simplified Block Diagram of the ONET4291T
SIGNAL PATH
The first stage of the signal path is a transimpedance amplifier that takes the photodiode current and converts it
into a voltage signal.
If the input signal current exceeds a certain value, the transimpedance gain is reduced by means of AGC
circuitry.
The second stage is a voltage amplifier that provides additional gain and converts its single-ended input voltage
into a differential data signal.
The third signal-path stage is the output buffer, which provides CML outputs with on-chip, 50-Ω back-termination
to VCC.
2
Copyright © 2011, Texas Instruments Incorporated
ONET4291T
www.ti.com
SLLSE82 – APRIL 2011
FILTER CIRCUITRY
The filter pin provides filtered VCC for the photodiode bias. The on-chip, low-pass filter for the photodiode VCC is
implemented using a filter resistor of 220 Ω and an internal 200-pF capacitor. The corresponding corner
frequency is below 4 MHz.
The supply voltage for the whole amplifier is filtered by means of an on-chip, 275-pF capacitor as well, thus
avoiding the necessity to use an external supply-filter capacitor.
DC INPUT CURRENT CANCELLATION, AGC, AND RSSI
The voltage drop across the internal photodiode supply-filter resistor is monitored by means of a dc input current
cancellation, AGC, and RSSI control circuit block.
If the dc input current exceeds a certain level, it is partially cancelled by means of a controlled current source.
This measure keeps the transimpedance amplifier stage within sufficient operating point limits for optimum
performance. Furthermore, disabling the dc input cancellation at low input currents leads to superior noise
performance.
The AGC circuitry lowers the effective transimpedance feedback resistor RF by means of a MOSFET device
acting as a controlled shunt. This prevents the transimpedance amplifier from being overdriven at high input
currents, which leads to improved jitter behavior within the complete input-current dynamic range. Because the
voltage drop across the supply-filter resistor is sensed and used by the AGC circuit, the photodiode must be
connected to a FILTER pad for the AGC to function correctly.
Finally, this circuit block senses the current through the filter resistor and generates a mirrored current, which is
proportional to the input signal strength. The mirrored current is available at the RSSI output and must be sunk to
ground (GND) using an external resistor. The RSSI gain can be adjusted by choosing the external resistor;
however, for proper operation, ensure that the voltage at the RSSI pad never exceeds VCC – 0.65 V.
BAND-GAP VOLTAGE AND BIAS GENERATION
The ONET4291T transimpedance amplifier is supplied by a single, 3.3-V supply voltage connected to the VCC
pad. This voltage is referred to GND.
On-chip band-gap voltage circuitry generates a supply-voltage-independent reference from which all other
internally required voltages and bias currents are derived.
Copyright © 2011, Texas Instruments Incorporated
3
ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
BOND PAD ASSIGNMENT
The ONET4291T is available as a bare die. The locations of the bond pads are shown in the following figure.
1
10
GND
GND
2
9
GND
OUT+
3
8
OUT–
VCC
4
7
RSSI
6
IN
FILTER
5
4291TAA
GND
M0033-04
BOND PAD DESCRIPTION
PAD
TYPE
DESCRIPTION
5
Analog
Bias voltage for photodiode (cathode). This pads connects through an internal 220-Ω resistor to
VCC and a 200-pF filter capacitor to ground (GND). The FILTER pad(s) must be connected to the
photodiode for the AGC to function.
1, 2, 9, 10
Supply
Circuit ground. All GND pads are connected on die. Bonding all pads is optional; however, for
optimum performance a good ground connection is mandatory.
NAME
NO.
FILTER
GND
IN
6
Analog input
OUT+
3
Analog output
Non-inverted data output. On-chip 50-Ω back-terminated to VCC.
OUT–
8
Analog output
Inverted data output. On-chip 50-Ω back-terminated to VCC.
Analog output current proportional to the input data amplitude. Indicates the strength of the
received signal (RSSI). Must be sunk through an external resistor to ground (GND). The RSSI
gain can be adjusted by choosing the external resistor; however, for proper operation, ensure
that the voltage at the RSSI pad never exceeds VCC – 0.65 V. If the RSSI feature is not used,
this pad must be bonded to ground (GND) to ensure proper operation.
RSSI
7
Analog output
VCC
4
Supply
4
Data input to TIA (photodiode anode)
3.3-V, +10%/–12% supply voltage
Copyright © 2011, Texas Instruments Incorporated
ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
ABSOLUTE MAXIMUM RATINGS
over operating free-air temperature range (unless otherwise noted)
VCC
Supply voltage
–0.3 V to 4 V
VFILTER, VOUT+, VOUT–,
VRSSI
Voltage at FILTER, OUT+, OUT–, RSSI
IIN
Current into IN
IFILTER
Current into FILTER
IOUT+, IOUT–
Continuous current at outputs
ESD
(1)
(2)
–0.3 V to 4 V
–0.7 mA to 2.5 mA
– 8 mA to 8 mA
ESD rating at all pins except IN
ESD rating at IN
(2)
– 8 mA to 8 mA
(3)
1.5 kV (HBM)
(3)
300 V (HBM)
TJ,max
Maximum junction temperature
Tstg
Storage temperature range
–65°C to 85°C
TA
Operating free-air temperature range
–40°C to 85°C
(1)
(2)
(3)
125°C
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating
Conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltage values are with respect to network ground terminal.
For optimum high-frequency performance, the input pin has reduced ESD protection.
RECOMMENDED OPERATING CONDITIONS
over operating free-air temperature range (unless otherwise noted)
MIN
NOM
MAX
VCC
Supply voltage
2.9
3.3
3.6
TA
Operating free-air temperature
–40
LFILTER,
LIN
Wire-bond inductor at pins FILTER and IN
CPD
Photodiode capacitance
UNIT
V
85
°C
0.8
nH
0.2
pF
DC ELECTRICAL CHARACTERISTICS
over recommended operating conditions (unless otherwise noted). Typical values are at VCC = 3.3 V and TA = 25°C.
PARAMETER
VCC
Supply voltage
IVCC
Supply current
VIN
Input bias voltage
ROUT
Output resistance
RFILTER
Photodiode filter resistance
Copyright © 2011, Texas Instruments Incorporated
TEST CONDITIONS
Average photodiode current IPD = 0
mA
Single-ended to VCC
MIN
TYP
MAX
2.9
3.3
3.6
11
17
25
0.85
1.05
V
50
60
Ω
40
220
UNIT
V
mA
Ω
5
ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
AC ELECTRICAL CHARACTERISTICS
over recommended operating conditions (unless otherwise noted). Typical values are at VCC = 3.3 V and TA = 25°C.
PARAMETER
iIN-OVL
AC input overload current
ARSSI
RSSI gain
TEST CONDITIONS
MIN
TYP
MAX
1
1.05
A/A
15
30
μA
2300
3200
3900
Ω
2.2
2.8
2
Resistive load to GND
(1)
0.95
RSSI output offset current (no light)
Z21
Small-signal transimpedance
Differential output; input current iIN =
50 μAp-p
fH,3dB
Small-signal bandwidth
iIN = 50 μAp-p
fL,3dB
Low-frequency, –3-dB bandwidth
–3 dB, input current iIN < 50 μAp-p
fH,3dB,RSSI
RSSI bandwidth
iN-IN
Input referred RMS noise
(2)
40
(3)
465
Input referred noise current density
Deterministic jitter
VOUT,D,MAX Maximum differential output voltage
(1)
(2)
(3)
(4)
6
GHz
70
(4)
iIN = 100 μAp-p (K28.5 pattern)
(4)
10
23
10
30
8
28
iIN = 2 mAp-p (K28.5 pattern)
13
42
200
310
140
nA
pA/√Hz
iIN = 1 mAp-p (K28.5 pattern)
Input current iIN = 1 mAp-p
kHz
MHz
590
8.8
iIN = 50 μAp-p (K28.5 pattern)
DJ
mAp-p
3.5
50 kHz–4 GHz
UNIT
psp-p
mVp-p
The RSSI output is a current output, which requires a resistive load to ground (GND). The voltage gain can be adjusted for the intended
application by choosing the external resistor. However, for proper operation of the ONET4291T, ensure that the voltage at RSSI never
exceeds VCC – 0.65 V.
The minimum small-signal bandwidth is specified over process corners, temperature, and supply voltage variation. The assumed
photodiode capacitance is 0.2 pF. The bond-wire inductance is 0.8 nH. The small-signal bandwidth strongly depends on environmental
parasitics. Careful attention to layout parasitics and external components is necessary to achieve optimal performance.
Input referred RMS noise is (RMS output noise)/(gain @ 100 MHz). The maximum input referred noise is specified over process
corners, temperature, and supply voltage variation.
At small input currents a significant portion of the deterministic jitter (DJ) is caused by duty-cycle distortion (DCD) due to residual offset
in the output signal. Because the TIA is not limiting, the DCD portion of the DJ is removed by the following limiting amplifier. The given
maximum values include DCD as well as six-sigma margin.
Copyright © 2011, Texas Instruments Incorporated
ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
TYPICAL CHARACTERISTICS
Typical operating condition is at VCC = 3.3 V and TA = 25°C.
UNFILTERER INPUT REFERRED NOISE
vs
AVERAGE INPUT CURRENT
UNFILTERED INPUT REFERRED NOISE
vs
AMBIENT TEMPERATURE
800
2400
Input Referred Noise Current − nARMS
Input Referred Noise Current − nARMS
2200
2000
1800
1600
1400
1200
1000
800
600
400
700
600
500
400
300
200
100
200
0
10
100
Average Input Current − µA
TA − Ambient Temperature − °C
G001
Figure 2.
Figure 3.
SMALL-SIGNAL TRANSIMPEDANCE
vs
AMBIENT TEMPERATURE
TRANSIMPEDANCE
vs
AVERAGE INPUT CURRENT
5000
4000
4500
3500
4000
3000
Transimpedance − Ω
Transimpedance − Ω
0
−40 −30 −20 −10 0 10 20 30 40 50 60 70 80 90
1k
3500
3000
2500
2500
2000
1500
2000
1000
1500
500
1000
−40 −30 −20 −10 0 10 20 30 40 50 60 70 80 90
TA − Ambient Temperature − °C
Figure 4.
Copyright © 2011, Texas Instruments Incorporated
G002
0
0
100 200 300 400 500 600 700 800 900 1000
Average Input Current − µA
G003
G004
Figure 5.
7
ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
Typical operating condition is at VCC = 3.3 V and TA = 25°C.
SMALL-SIGNAL BANDWIDTH
vs
AMBIENT TEMPERATURE
SMALL-SIGNAL TRANSFER CHARACTERISTICS
70
3.00
2.95
68
Transimpedance − dBΩ
2.90
Bandwidth − GHz
2.85
2.80
2.75
2.70
2.65
66
64
62
60
2.60
58
2.55
2.50
−40 −30 −20 −10 0 10 20 30 40 50 60 70 80 90
TA − Ambient Temperature − °C
56
100
1k
10k
f − Frequency − MHz
G006
G005
Figure 6.
Figure 7.
RSSI OUTPUT CURRENT
vs
AVERAGE INPUT CURRENT
DETERMINISTIC JITTER
vs
INPUT CURRENT
16
1200
14
Deterministic Jitter − ps
RSSI Output Current − µA
1000
800
600
400
200
12
10
8
6
4
2
0
0
0
200
400
600
800
1000
1200
0
400
800
1200
Input Current − µAP−P
Average Input Current − µA
G007
Figure 8.
8
1600
2000
G008
Figure 9.
Copyright © 2011, Texas Instruments Incorporated
ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
Typical operating condition is at VCC = 3.3 V and TA = 25°C.
OUTPUT EYE DIAGRAM AT 4.25 Gbps AND 20-μAp-p
INPUT CURRENT
Differential Output Voltage − 10 mV/Div
Differential Output Voltage − 10 mV/Div
OUTPUT EYE DIAGRAM AT 4.25 Gbps AND 10-μAp-p
INPUT CURRENT
Time − 50 ps/Div
Time − 50 ps/Div
G009
G010
OUTPUT EYE DIAGRAM AT 4.25 Gbps AND 100-μAp-p
INPUT CURRENT
OUTPUT EYE DIAGRAM AT 4.25 Gbps AND 1-mAp-p INPUT
CURRENT
Differential Output Voltage − 50 mV/Div
Figure 11.
Differential Output Voltage − 50 mV/Div
Figure 10.
Time − 50 ps/Div
Time − 50 ps/Div
G011
Figure 12.
Copyright © 2011, Texas Instruments Incorporated
G012
Figure 13.
9
ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
Typical operating condition is at VCC = 3.3 V and TA = 25°C.
Differential Output Voltage − 50 mV/Div
OUTPUT EYE DIAGRAM AT 4.25 Gbps AND 2-mAp-p INPUT CURRENT
Time − 50 ps/Div
G013
Figure 14.
10
Copyright © 2011, Texas Instruments Incorporated
ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
APPLICATION INFORMATION
Figure 15 shows an application circuit for an ONET4291T being used in a typical fiber-optic receiver. The
ONET4291T converts the electrical current generated by the PIN photodiode into a differential output voltage.
The FILTER input provides a dc bias voltage for the PIN that is low-pass filtered by the combination of the
internal 220-Ω resistor and 200-pF capacitor. Because the voltage drop across the 220-Ω resistor is sensed and
used by the AGC circuit, the photodiode must be connected to a FILTER pad for the AGC to function correctly.
The RSSI output is used to mirror the photodiode average current and must be connected via a resistor to GND.
The voltage gain can be adjusted for the intended application by choosing the external resistor. However, for
proper operation of the ONET4291T, ensure that the voltage at RSSI never exceeds VCC – 0.65 V. If the RSSI
output is not used, it must be grounded.
The OUT+ and OUT– pads are internally terminated by 50-Ω pullup resistors to VCC. The outputs must be
ac-coupled (e.g., using C1 = C2 = 0.1 μF) to the succeeding device. An additional capacitor, CNBW, which is
differentially connected between the two output pins OUT+ and OUT–, can be used to limit the noise bandwidth
and thus optimize the noise performance.
C1
0.1 mF
OUT+
3
4
5
6
220 W
200 pF
2
ONET
4291T
1
CNBW
0 to 2 pF
Optional
PAD#1
VCC
275 pF
10
7
8
9
C2
0.1 mF
OUT–
RSSI
GND
S0097-03
Figure 15. Basic Application Circuit
ASSEMBLY RECOMMENDATIONS
When packaging the ONET4291T, careful attention to parasitics and external components is necessary to
achieve optimal performance. Recommendations that optimize performance include:
1. Minimize total capacitance on the IN pad by using a low-capacitance photodiode and paying attention to
stray capacitances. Place the photodiode close to the ONET4291T die to minimize the bond wire length and
thus the parasitic inductance.
2. Use identical termination and symmetrical transmission lines at the ac-coupled differential output pins OUT+
and OUT–. A differential capacitor CNBW can be used to limit the noise bandwidth.
3. Use short bond-wire connections for the supply terminals VCC and GND. Supply-voltage filtering is provided
on-chip. Filtering can be improved by using an additional external capacitor.
Copyright © 2011, Texas Instruments Incorporated
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ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
CHIP DIMENSIONS AND PAD LOCATIONS
1
10
2
9
3
8
5
y
4
Origin
0,0
4291TAA
1180 mm
Overall chip dimensions and depiction of the bond-pad locations are given in Figure 16. Layout of the chip
componentry is shown in Figure 17.
6
7
780 mm
x
M0033-05
Figure 16. Chip Dimensions and Pad Locations
y
ET
1TA
1180 mm
PAD#1
Origin
0,0
780 mm
x
M0033-06
Figure 17. Chip Layout
12
Copyright © 2011, Texas Instruments Incorporated
ONET4291T
SLLSE82 – APRIL 2011
www.ti.com
Table 1. Pad Locations and Descriptions for the ONET4291T
PAD
COORDINATES
SYMBOL
TYPE
DESCRIPTION
x (μm)
y (μm)
1
100
1063
GND
Supply
Circuit ground
2
100
938
GND
Supply
Circuit ground
3
100
570
OUT+
Analog output
Non-inverted data output
4
90
127
VCC
Supply
3.3-V supply voltage
5
265
127
FILTER
Analog
Bias voltage for photodiode
6
515
127
IN
Analog input
Data input to TIA
7
690
127
RSSI
Analog output
RSSI output signal
8
680
570
OUT–
Analog output
Inverted data output
9
680
938
GND
Supply
Circuit ground
10
680
1063
GND
Supply
Circuit ground
DIE INFORMATION
Die size: 1180 μm × 780 μm
Die thickness: 8 mils (203 μm)
Pad metallization: 99.5% Al, 0.5% Cu
Pad size: octagonal pads 120 μm × 100 μm
Passivation composition: 6000-Å silicon nitride
Backside contact: none
Die ID: 4291TAA
TO46 LAYOUT EXAMPLES
2.
54
m
m
Examples for layouts (top view) in 5-pin and 4-pin TO46 headers are given in Figure 18 and Figure 19,
respectively.
GND
OUT+
OUT–
VCC
RSSI
M0034-03
Figure 18. TO46 5-Pin Layout Example Using the ONET4291T
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ONET4291T
SLLSE82 – APRIL 2011
2.
54
m
m
www.ti.com
VCC
OUT–
OUT+
GND
M0034-04
Figure 19. TO46 4-Pin Layout Example Using the ONET4291T
14
Copyright © 2011, Texas Instruments Incorporated
PACKAGE OPTION ADDENDUM
www.ti.com
24-Apr-2019
PACKAGING INFORMATION
Orderable Device
Status
(1)
ONET4291TY
ACTIVE
Package Type Package Pins Package
Drawing
Qty
DIESALE
Y
0
340
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
TBD
Call TI
Call TI
Op Temp (°C)
Device Marking
(4/5)
-40 to 85
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of