【正文】 ngth [m], d is the wire diameter [m], p, is the relative permeability and 6 is the skin effect factor. For example, a 1 mm length of 18 pm diameter wire can be approximated as a nH inductor, neglecting ground plane effects. The electrical design of our 10 Ghis modules was focused primarily on the reduction of inductive and capacitive parasitics such that the optimum performance of the two semiconductors could be achieved. The identification and control of such parasitics was acplished by using microwave amplifier analytical techniques. The intrinsic microwave performance of the pin and APD detectors were previously presented. Analysis of the HEMT TIA was acplished by utilizing the measured sparameters of the chip. The TIA sparameters were measured out to 16 GHz in 1 GHz increments. The TIA chip was fust analyzed for stability, which can be defined [lo] as its resistance to oscillate. Ideally it is desirable to have an unconditionally stable amplifier, which means that it will not oscillate with any passive source or load impedances. 21 1 1999 Electronic Components and Technology Conference PD CHIP I U L4 I I I I * Figure 8: Linear electrical model of 10 Gb/s receiver Using the amplifier sparameters one can perform a stability analysis. Two microwave factors, K and A, can be used to determine amplifier stability. From [lo] a convenient way of expressing the necessary and sufficient conditions for unconditional stability is K Z 1 and ]A1 1, where 1 Isif P22? + IA? (6) K= 2 l~l$2ll A = siiszz si821 (7) Using (6) and (7), the TIA chip was calculated to be unconditionally stable over the entire bandwidth out to 16 GHz. This unconditional stability is certainly a beneficial attribute, however a critical parasitic needs to be considered in the stability analysis. The grounding of wide bandwidth, highgain amplifiers is usually critical for achieving the maximum microwave performance. Inductance due to bonding wires can cause unwanted feedback, resonances and possibly oscillations. The GaAs HEMT TIA used in our 10 Gb/s receivers is fabricated on a semiinsulating GaAs substrate and hence relies on multiple wirebonds for electrical grounding. The circuit model in Fig. 8 includes a TIA ground inductance, labeled as L5, which models the effect of the grounding wirebonds. These wirebonds are kept as short as possible in the receiver module, however a small inductance can still be detrimental. A stability analysis of the TIA chip was repeated using (6) and (7), however the effect of L5 was included. The analysis indicates the TIA chip remains unconditionally stable with values of L5 5 20 pH. As an example of stability problems associated with TIA ground inductance, Fig. 9 illustrates a stability analysis with an L5 value of 30 pH. The Smith chart in Fig. 9 shows the input stability circles for the potentially unstable frequencies of GHz through GHz, as well as the simulated source impedance presented to the TIA chip. The center, C, and radius, r, of the input stability circles can be calculated [IO] as (9) As shown in the simulation in Fig. 9, the source impedance presented to the TIA by the PD chip and parasitics may result in an unstable output with 30 pH of TIA ground inductance. Unstable Reaion rce edance Figure 9 Input stability with 30 pH ground inductance Inductance in the TIA ground may cause other undesirable electrical performance in addition to potential instability. Values of L5 5 20 pH may result in an unconditionally stable device, however the electrical performance may still exhibit degradation. Simulations of the receiver frequency response and group delay as a function of ground inductance L5 were performed. Fig. 10 and Fig. 11 illustrate the peaking effect due to L5 on both parameters. The increase in group delay at frequencies within the operating bandwidth will result in increased eye pattern jitter and can degrade BER performance. Typical 10 Gb/s receiver specifications require +/ dB maximum gain flatness and +/ 40 ps maximum group delay. The simulations indicate that 2 10 pH of TIA ground inductance is required in order to meet these specifications. This low value of ground inductance is achieved by wirebonding multiple TIA ground connections directly to the metal heat sink, which is precisely machined around the IC. Referring to Fig. 8, there are several other parasitics and electrical ponent values which can effect the microwave performance. From (2) the capacitance of the PD chip has an impact on receiver bandwidth. The PD contact resistance。 therefore, the structure is designed to inject photoexcited holes from the InGaAs into the InP multiplication region to seed the (a) photodiode (b) avalanche photodiode ilnGaAs ABSORPTION *.lP SUBSTRATE Figure 5: (a)pin and (h) APD device structures Figure 6: APD 3dB bandwidth as a function of device gain. Bandwidth enhancement for 10M05 is due to parasitic inductive peaking。High Performance 10 Gb/s PIN and APD Optical Receivers Jim Rue, Mark Mer, Nitish Agrawal, Stephen Bay and William Sherry EPITAXX, Inc. 7 Graphics Drive West Trenton, NJ 08628 Abstract The increasing market demand for highspeed optical transmission systems at rates of IO Gbls bas resulted in technical challenges for suppliers of highperformance, manufacturable optoelectronic ponents and systems. In particular, the performance of the InP semiconductor devices, integrated circuits (ICs) and hybrid IC modules strongly influences the achievable transmission capability. An optical receiver design is presented which incorporates an InPbased pin (positiveintrinsicnegative) photodetector (PD) or avalanche photodetector (APD) and a GaAs high electron mobility transistor (HEMT) preamplifier integrated