OPA375 datasheet(33/67 Pages) TI2

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9.2.2 Detailed Design Procedure

The transfer function defining the relationship between VOUT and the AC input signal is shown in Equation 1.

OUT

u ¨

(1)

The required gain can be calculated based on the expected input signal level and desired output level as shown

in Equation 2.

126

7.93

OUT

RMS

OPA

RMS

(2)

Select a standard 10-kΩ feedback resistor and calculate RG from Equation 3.

78.7

(closest standard value)

126

OPA

: o

(3)

To minimize the attenuation in the desired passband from 300 Hz to 3 kHz, set the upper (fH) and lower (fL) cutoff

frequencies outside of the desired bandwidth as:

fL = 200 Hz

(4)

and

fH = 5 kHz

(5)

Select CG to set the fL cutoff frequency using Equation 6.

10.11

78.7

200

: u

(6)

Select CF to set the fH cutoff frequency using Equation 7.

3.18

3.3

(Standard Value)

kHz

: u

(7)

The input signal cutoff frequency must be set low enough such that low-frequency sound waves still pass

through. Therefore select CIN to achieve a 30-Hz cutoff frequency (fIN) using Equation 8.

(Standard Value)

(

)

100

: u

(8)

The measured transfer function for the microphone preamplifier circuit is shown in Figure 9-2 and the measured

THD + N performance of the microphone preamplifier circuit is shown in Figure 9-3.

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OPA375, OPA2375

SBOS886E – NOVEMBER 2017 – REVISED AUGUST 2021

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