he BER is ratio of bits in error to total bits transferred for a given transmission interval. Full details of the measurement are found in [Mars-94a]. This setup for proton testing is similar to that shown in figure 11 for fiber-channel transceiver hardware, and the need for software controlled data collection and logging applies here too. Proton Induced Bit Errors Proton ionization tracks or reaction recoils generate charge in detectors. This "0" is "1" is not This "0" may corrupted corrupted be corrupted DECISION LEVEL (8(0) Decision Points PROBABILITY Figure 13. The reverse biased disk-shaped planar collects charge that is deposited by direct ionization from protons. Resulting current pulses sensed in the receiver circuit decay with an RC time constant determined by the circuit bandwidth. Data can be disrupted if ion-induced current exceeding the threshold current is sensed at the critical mid-bit decision when a "0" is being transmitted. IV-32 Proton BER Measurement PN Data Sequence Generator, 27-1 Sequence 0.2, 0.4, or 1 Gbps Recovery BER Calculation Optical Data Proton Modulator 1300 nm Laser Oscilloscope Shield Amplifier Optical Attenuator Photodiodo Clock Recovery Under Lightwave Power Meter Data Regenerator Figure 14. This illustrates a typical test setup for measuring link bit-error-rate performance. details of the measurement are found in [Mars-94a]. The automated test set uses commercially available bit error rate test equipment. The tester was set to generate a serial pseudo random numeric (PN or PRN) sequence of (27-1) bits in length. Data rates of 200, 400, and 1000 Mbps were established by an external waveform generator. The fiber link included a programmable attenuator SO that the desired optical power level could be adjusted over the range of -30 dBm to 0 dBm (or 1 uW to 1 mW). The optical power was monitored by an external light wave meter or coupled onto the surface of the photodiode under test. Light was launched onto the photodiode using a 3- axis micro-manipulator stage, and coupling effici