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A broadband test setup for differential mode measurement of infrared photodiodes in TO-8 package

We present a test setup for broadband balanced characterization of infrared photodiodes mounted inside TO-8 package. The test setup is composed of a four-port detector test fixture, a broadband three-port balun, a pair of bias networks and a pair of short SMA semirigid cables. It is dedicated for noise spectral density measurements and time-domain opto-electrical measurements involving impulse laser light stimulation. To provide high common mode rejection ratio (CMRR), we pursue symmetry in the test setup by carefully selecting a way the setup elements are assembled so as minimize impact of signal imbalance. We employ a vector network analyzer to verify properties of our three-port test setup by comparing two groups of its scattering parameters: one simulated with ADS software using S-matrices individually measured for each setup element and the other one determined from one-port calibration measurements in the test setup with tiny short-open-load calibration standards mounted on a TO-8 header. According to obtained results, the test setup provides the CMRR over 40 dB in the bandwidth extending from 100 kHz up to 3 GHz.