Pulse response tuning of high speed InGaAs thin film MSM photodetector using external RCL loads

Abstract

Practical, packaged photodetectors (PDs) must be interfaced to bias and transmission lines, which introduce parasitics. These parasitics (resistance, capacitance and inductance) can be used to shape the temporal and frequency response of packaged photodetectors. Thus, the bias circuitry, external passives, and high speed interconnections must be carefully designed to produce the desired response in a packaged photodetector. Applications dictate the desired PD characteristics, which are generally either a flat frequency response, or a fast, ring-free impulse response. In this paper, the effects of the parasitic resistance, capacitance, and inductance are studied to affect the intrinsic response of photodetectors for a flat frequency response or a fast ring-free impulse response. For the optical transmission of microwave and millimeter wave RF signals, such as remote antennas or radar arrays, a flat frequency response is critical. A flat frequency response can be obtained from controlled ringing in the temporal domain. This paper explores the control of ringing in the temporal domain using varied external loads. A fast fall time, ring-free pulse is useful for digital communications applications where ringing can degrade the bit error rate. Fourier transforms show that a ring-free impulse response has a characteristic fall-off at high frequencies. However, this fall-off is detrimental for frequency domain applications, so the optimization condition for the inductance and capacitance is different for these applications. This paper explores the suppression of the impulse response tail by varying the external loads.