ATA01504D1C

AGC Transimpedance Amplifier SONET OC-3 FEATURES · · · · · · Single +5 Volt Supply TO Package Compatible Automatic Gain Control -38 dBM Sensitivity 0 dBm Overload 175 MHz Bandwidth ATA01504 PRELIMINARY DATA SHEET-Rev 1 APPLICATIONS · · · SONET OC-3/SDH STM-1 (155 Mb/s) Receiver FDDI, Ethernet Fiber LAN Low Noise RF Amplifier D1C PRODUCT DESCRIPTION The ANADIGICS ATA01504 is a 5V low noise transimpedance amplifier with AGC designed to be used in OC-3/STM-1 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 ATA01504 offers a bandwidth of 175MHz, a dynamic range of 38dB and an alternate pad layout as compared to the ATA01501. It is manufactured in a GaAs MESFET process and is available in bare die form. VDD AGC 19K 70K + CAGC 4.5 pF - 45 VGA + 0.8 VOUT IIN GND or neg.supply GND US PATENT 5442321,5602510,5047728 Photodector cathode must be connected to IIN for proper AGC operation Figure 1: Equivalent Circuit 08/2001 ATA01504 Figure 2: Bonding Pad Layout Table 1: Pad Description PAD V DD IIN VOUT C AGC D escription V DD TIA Input C urrent TIA Output Voltage External AGC C apaci tor C omment Posi ti ve supply for i nput gai n stage C onnect detector cathode for proper operati on Requi res external D C block 70K* (C AGC *4.5 pF) = AGC Ti me C onstant ELECTRICAL CHARACTERISTICS Table 2: Absolute Maximum Ratings V DD IIN TA TS 7.0 V 5 mA Operati ng Temp. - 40 oC to 125 oC Storage Temp. - 65 oC to 150 oC 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 1 08/2001 ATA01504 Table 3: Electrical Specifications (1) (TA = 25°C, VDD =+5.0V + 10%, CDIODE + CSTRAY = 0.5 pF, Det. cathode to IIN) PAR AMETER Transresi stance (RL=¥,IDC=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. 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 available for power supply bypassing. Traces that can be made short should be made short, and the utmost care should be taken to maintain very low capacitance at the photodiode TIA interface (IIN), as excess capacitance at this node will cause a degradation in bandwidth and sensitivity (see Bandwidth vs. CT curves). 4 210 Bandwith (MHz) 200 190 180 170 160 150 B(3dB) A / 2 π Rf (Cin +Ct) ≈ VDD = 5.5 V VDD = 5.0 V VDD = 4.5 V 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 CT(pF) Figure 4: Bandwidth vs. CT Note: All performance curves are typical @ TA =25 °C unless otherwise noted. PRELIMINARY DATA SHEET - Rev 1 08/2001 ATA01504 IIN connection (refer to the equivalent circuit diagram) Bonding the detector cathode to IIN (and thus drawing current from the ATA01504) 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. 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. 10 8 7 I IIN 6 50 Transimpedance (K Ohm) 9 5 4 3 2 1 heavy AGC Output Collapse VDD = 5.5 V VDD = 4.5 V VDD = 5.5 V Linear Region Rf I IN VOUT -2.1 - 1.6 -1.1 - 0.6 - 0.1 IIN (mA DC) Figure 5: Transimpedance vs. IIN VDD = 4.5 V -4 -3 -2 -1 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 Bandwidth vs IIN 1 .5 BANDWIDTH (GHz) 1 .3 IIN ( mA DC) Figure 7: VOUT vs. IIN VDD=5.5 V 1 .1 0 .9 0 .7 VDD=4.5 V 1501 0 .5 IIN .3 50 0 0 .1 - 2.1 - 1.6 - 1.1 IIN (mA DC) - 0.6 - 0.1 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. Figure 6: Bandwidth vs. IIN PRELIMINARY DATA SHEET - Rev 1 08/2001 VOUT(Volts) 5 ATA01504 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 b its. The ATA01504D1C 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 (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. 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 110 MHz lowpass filter at the output of the TIA) divided by the AC transresistance. 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. 14 Hz Rf CT Figure 9: Phase (IIN to VOUT) 50 10 pA/ 6 2 CT=1.0pF CT =0.5pF 1 10 100 1000 - 0.1 Frequency (MHz) Figure 8: Input Referred Noise Spectral Density AGC Capacitor It is important to select an external AGC capacitor of high quality and appropriate size. The ATA01504D1C 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 155 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. 6 PRELIMINARY DATA SHEET - Rev 1 08/2001 ATA01504 NOTES PRELIMINARY DATA SHEET - Rev 1 08/2001 7 ATA01504 ORDERING INFORMATION PAR T N U MB ER ATA01504D 1C PAC K AGE OPTION D 1C PAC K AGE D ESC R IPTION 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 Mktg@anadigics.com 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 product’s 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 1 08/2001