ATA06211 AGC Transimpedance Amplifier SONET OC-12 PRELIMINARY DATA SHEET-Rev 4 FEATURES · Single +5 Volt Supply · Automatic Gain Control · -32 dBm Sensitivity · 0 dBm Optical Overload · 550 MHz Bandwidth APPLICATIONS · SONET OC-12 /SDH STM-4 (622Mb/s) Receiver · FITL · BISDN · Workstation Interconnects · Low Noise RF Amplifier D1 PRODUCT DESCRIPTION The ANADIGICS ATA06211 is a 5V low noise transimpedance amplifier with AGC designed to be used in OC-12/STM-4 fiber optic links. The device is used in conjunction with a photodetector (PIN diode or avalanche photodiode) to convert an optical signal into an output voltage. The ATA06211 offers a bandwidth of 550MHz and a dynamic range of 32dB. It is manufactured in a GaAs MESFET process and is available in bare die form. VDD1 VDD2 AGC 19 K 70K CAGC + 4pF IIN GND or neg.supply - 35 + 0.8 VGA US PATENT VOUT GND CBY Photodector cathode must be connected to IIin for proper AGC operation IN Figure 1: Equivalent Circuit 08/2001 ATA06211 Figure 2: Bonding Pad Layout Table 1: ATA06211D1C Pad Description PAD D ESC R IPTION C OMMEN T V DD1 V DD1 Posi ti ve supply for i nput gai n stage V DD2 V DD2 Posi ti ve supply for second gai n stage TIA Input C urrent C onnect detector cathode for proper operati on VOUT TIA Output Voltage Requi res external D C block C AGC External AGC C apaci tor 70K* C AGC = AGC Ti me C onstant C BY Input Gai n Stage Bypass C apaci tor >56 pF IIN ELECTRICAL CHARACTERISTICS Table 2: Absolute Maximum Ratings V DD1 7.0 V V DD2 7.0 V IIN 5 mA TA Operati ng Temp. - 40 °C to 125 °C TS Storage Temp. - 65 °C to 150 °C Stresses in excess of the absolute ratings may cause permanent damage. Functional operation is not implied under these conditions. Exposure to absolute ratings for extended periods of time may adversely affect reliability. 2 PRELIMINARY DATA SHEET - Rev 4 08/2001 ATA06211 Table 3: Electrical Specifications (1) (TA = 25°C, VDD =+5.0V + 10%, CDIODE + CSTRAY = 0.5 pF, Det. cathode to IIN) PAR AMETER MIN Transresi stance (RL=¥ ,IDC<500nA) Transresi stance (RL=50 W ) (1) Bandwi dth -3dB 2.5 500 Input Resi stance (2) Output Resi stance 30 TYP MAX U N IT 6 KW 3 KW 550 MHz 280 W 50 60 W Supply C urrent 15 30 45 mA Input Offset Voltage 1.4 1.6 1.9 Volts Output Offset Voltage AGC Threshold (IIN) Opti cal Overload (3) 60 -3 (4) 1.8 Volts 100 mA 0 dB m Input Noi se C urrent (5) 50 AGC Ti me C onstant 16 m se c (6) Offset Voltage D ri ft 60 nA ±1 mV/ º C -31 -32 dB m Operati ng Voltage Range + 4.5 + 5.0 Operati ng Temperature Range - 40 Opti cal Sensi ti vi ty (7) + 6.0 Volts 85 ºC Notes: 1. f = 50MHz 2. Measured with Iin below AGC Threshold. During AGC, input impedance will decrease proportionally to Iin. 3. Defined as the Iin where Transresistance has decreased by 50%. 4. See note on Indirect Measurement of Optical Overload. 5. See note on Measurement of Input Referred Noise Current. 6. CAGC = 220 pF 7. Parameter is guaranteed (not tested) by design and characterization data @622 Mb/s, assuming dectector responsivity of 0.9. PRELIMINARY DATA SHEET - Rev 4 08/2001 3 ATA06211 APPLICATION INFORMATION VDD 56pF 56pF GND ATA06211D1C Bonding Pads VDD2 925 um VDD1 GND 7I GND PIN IIN 1992 GND VOUT OUT GND GND GND CBY CBY GND CAGC GND 1250 um 56pF 56pF Figure 3: Typical Bonding Diagram General Layout Considerations Since the gain stages of the transimpedance amplifier have an open loop bandwidth in excess of 1.0 GHz, it is essential to maintain good high frequency layout practices. To prevent oscillations, a low inductance RF ground plane should be made the utmost care should available for power supply bypassing. Traces that can be made short should be made short, and be taken to maintain very low capacitance at the photodiode-TIA interface (IIN), as excess capacitance at this node will cause a 4 degradation in bandwidth and sensitivity (see Bandwidth vs. CT curves). C T = 0.5 pF 0.90 Bandwidth (MHz) Power Supplies and General Layout Considerations The ATA06211D1C may be operated from a positive supply as low as + 4.5 V and as high as + 6.0 V. Below + 4.5 V, bandwidth, overload and sensitivity will degrade, while at + 6.0 V, bandwidth, overload and sensitivity improve (see Bandwidth vs. Temperature curves). Use of surface mount (preferably MIM type capacitors), low inductance power supply bypass capacitors (>=56pF) are essential for good high frequency and low noise performance. The power supply bypass capacitors should be mounted on or connected to a good low inductance ground plane. V = 5.5 V 0.80 0.70 DD V = 5.0 V DD 0.60 0.50 V = 4.5 V 0.40 -40 10 DD 60 85 Temperature (O C) Figure 4: Bandwidth vs. Temperature Note: All performance curves are typical @ TA =25 C° unless otherwise noted. PRELIMINARY DATA SHEET - Rev 4 08/2001 ATA06211 800 1.1 VDD = 5.5 V VDD = 5.5 V 700 1.0 VDD = 5.0 V 600 0.9 0.8 500 VDD = 4.5 V 400 VDD = 4.5 V 0.7 0 0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 1 .4 0.5 2.1 - 1.6 - 1.1 Figure 5: Bandwidth vs. CT IIN 4 3 50 2 VDD = 5.5 V 1 VDD = 4.5 V - 1.6 -1.1 - 0.6 Transimpedance (K Ohm) 5 I - 0.6 - 0.1 IIN (mA DC) IIN Connection (Refer to the equivalent circuit diagram.) Bonding the detector cathode to IIN (and thus drawing current from the ATA06211) improves the dynamic range. Although the detector may be used in the reverse direction for input currents not exceeding 25 mA, the specifications for optical overload will not be met. Rf 50 1 .6 CT (pF) -2.1 0.6 IIN 300 BANDWIDTH (MHz) 1.2 B(3dB) A / 2 π Rf (Cin +Ct) Figure 7: Bandwidth vs. IIN VOUT Connection The output pad should be connected via a coupling capacitor to the next stage of the receiver channel (filter or decision circuits), as the output buffers are not designed to drive a DC coupled 50 ohm load (this would require an output bias current of approximately 36 mA to maintain a quiescent 1.8 Volts across the output load). If VOUT is connected to a high input impedance decision circuit (>500 ohms), then a coupling capacitor may not be required, although caution should be exercised since DC offsets of the photo detector/TIA combination may cause clipping of subsequent gain or decision circuits. heavy AGC Output Collapse VDD =5.5 V Linear Region - 0.1 Rf IIN (mA DC) IIN VOUT Figure 6: Transimpedance vs. IIN VDD=4.5 V -4 -3 -2 3.4 3.2 3.0 2.9 2.7 2.5 2.4 2.2 2.0 1.9 1.7 1.5 1.4 1.2 1.0 0.8 0.7 0.5 0.3 0.2 0.0 VOUT(Volts) Bandwith (MHz) 900 -1 IIN(mA DC) Figure 8: VOUT vs. IIN PRELIMINARY DATA SHEET - Rev 4 08/2001 5 Input Offset Voltage ATA06211 1.9 1.85 1.8 1.75 1.7 1.65 1.6 1.55 1.5 - 40 VDD = 5.5 V VDD = 5.0V Measurement of Input Referred Noise Current The Input Noise Current is directly related to sensitivity . It can be defined as the output noise voltage (Vout), with no input signal, (including a 450 MHz lowpass filter at the output of the TIA) divided by the AC transresistance. VDD = 4.5V 10 (see VOUT vs IIN figure) from the TIA and determining the point of output voltage collapse. Also the input node virtual ground during heavy AGC is checked to verify that the linearity (i.e. pulse width distortion) of the amplifier has not been compromised. 60 Temperature (OC) Sensitivity and Bandwidth In order to guarantee sensitivity and bandwidth performance, the TIA is subjected to a comprehensive series of tests at the die sort level (100% testing at 25 oC) to verify the DC parametric performance and the high frequency performance (i.e. adequate |S21|) of the amplifier. Acceptably high |S21| of the internal gain stages will ensure low amplifier input capacitance and hence low input referred noise current. Transimpedance sensitivity and bandwidth are then guaranteed by design and correlation with RF and DC die sort test results. Indirect Measurement of Optical Overload Optical overload can be defined as the maximum optical power above which the BER (bit error rate) increases beyond 1 error in 10 10 bits. The ATA06211D1C is 100% tested at die sort by a DC measurement which has excellent correlation with an PRBS optical overload measurement. The measurement consists of sinking a negative current 6 Hz 6.5 pA/ CBY Connection The CBY pad must be connected via a low inductance path to a surface mount capacitor of at least 56pF (additional capacitance can be added in parallel with the 56 pF or 220 pF capacitors to improve low frequency response and noise performance). Referring to the equivalent circuit diagram and the typical bonding diagram, it is critical that the connection from CBY to the bypass capacitor use two bond wires for low inductance, since any high frequency impedance at this node will be fed back to the open loop amplifier with a resulting loss of transimpedance bandwidth. Two pads are provided for this purpose 7.5 4.5 Rf 5.5 CT 3.5 50 CT=1.0pF 2.5 1.5 CT =0.5pF - 0.1 1 10 100 1000 Frequency (MHz) Figure 10: Input Referred Noise Spectral Density Input Referred Noise in (nA RMS) Figure 9: Input Offset Voltage vs. Temperature Input referred noise test circuit 70 VDD = 4.5 V 25dB 60 58 0.5pF TIA 400 MHz LPF 54 VDD = 5.5V 50 η(dBm) = 10 LOG 46 42 -40 0 40 6500in R 80 O Temperature ( C) FIgure 11: Input Referred Noise vs Temperature PRELIMINARY DATA SHEET - Rev 4 08/2001 ATA06211 AGC Capacitor It is important to select an external AGC capacitor of high quality and appropriate size. The ATA06211D1C has an on-chip 70 KW resistor with a shunt 4 pF capacitor to ground. Without external capacitance the chip will provide an AGC time constant of 280 nS. For the best performance in a typical 622 MB/s SONET receiver, a minimum AGC capacitor of 56pF is recommended. This will provide the minimum amount of protection against pattern sensitivity and pulse width distortion on repetitive data sequences during high average optical power conditions. Conservative design practices should be followed when selecting an AGC capacitor, since unit to unit variability of the internal time constant and various data conditions can lead to data errors if the chosen value is too small. Phase Response At frequencies below the 3dB bandwidth of the device, the transimpedance phase response is characteristic of a single pole transfer function (as shown in the Phase vs Frequency curve). The output impedance is essentially resistive up to 1000 MHz. Degrees 180 200 Rf 220 240 VOUT IIN 0.5pF 50 100 150 Frequency (MHz) Figure 12: Phase (IIN to VOUT) PRELIMINARY DATA SHEET - Rev 4 08/2001 7 ATA06211 ORDERING INFORMATION PAR T N U MB ER PAC K AGE OPTION PAC K AGE D ESC R IPTION ATA06211D 1C D 1C Die ANADIGICS, Inc. 141 Mount Bethel Road Warren, New Jersey 07059, U.S.A Tel: +1 (908) 668-5000 Fax: +1 (908) 668-5132 http://www.anadigics.com [email protected] IMPORTANT NOTICE ANADIGICS, Inc. reserves the right to make changes to its products or to discontinue any product at any time without notice. The product specifications contained in Advanced Product Information sheets and Preliminary Data Sheets are subject to change prior to a products formal introduction. Information in Data Sheets have been carefully checked and are assumed to be reliable; however, ANADIGICS assumes no responsibilities for inaccuracies. ANADIGICS strongly urges customers to verify that the information they are using is current before placing orders. WARNING ANADIGICS products are not intended for use in life support appliances, devices, or systems. Use of an ANADIGICS product in any such application without written consent is prohibited. 8 PRELIMINARY DATA SHEET - Rev 4 08/2001