ZHCSJ01B January 2019 – August 2019 OPA1671
PRODUCTION DATA.
The preamplifier circuit uses a noninverting gain configuration to allow for high input impedance, with independent gain-setting resistor values. DC bypass is accomplished with C2 and C3, with the low frequency poles set by C2, R4, C3 and R5; see Equation 1 and Equation 2.
The filter cutoff frequency is determined by a higher frequency pole, set by R5 and C4.
The gain of the circuit in the passband is set by R5 and R6.
The ouput noise of the circuit (ignoring the electret microphone intrinsic noise and impedance) is the RSS average noise contribution from R5 and the input voltage noise of OPA1671. R5 was selected for minimal noise contribution without requiring a dc blocking cap. (C3) larger than 10 µF. See Equation 5 for the output noise density calculation at 10 kHz.