T&M: TIPS T his article will introduce a trial to jigs, and materials commonly available, and also includes some workarounds to improve the measurement to finally achieve 50fA. First, we measure the input capacitance for bias current measurement and the variation of output voltage with charging of the input capacitance under the condition of 125°C. We also attempt to derive the bias current value from the recreate the measurement in AN-1373 using commercial-grade lab equipment, measured output voltage. Finally, we will try to improve the measurement environment based on the measurement results. Capacitive integration measurement According to AN-1373, the input capacitance (C p ) of the ADA4530-1 must be measured first in order to use the capacitance integral measurement method. We will perform this experiment using the ADA4530-1R- EBZ-BUF with the ADA4530-1 configured in buffer mode. Next, we calculate the input current (I B+ ). Specifically, using the circuit configuration shown in Figure 1, when the SW in the test box is turned from ON (grounded to GND) to OFF (open), I B+ flows into the C p . The output voltage rises as I B+ charges C p , so the value of I B+ can be calculated by monitoring
Figure 1. A diagram of the capacitive integration measurement method.
Figure 2. Calculation of Cp using series resistance of input.
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