TS472_06 Datasheet, PDF (14/24 Pages) STMicroelectronics – Very low noise microphone preamplifier with 2.0V bias output and active low standby mode

Application information
5
Application information
TS472
5.1
Differential configuration principle
The TS472 is a full-differential input/output microphone preamplifier. The TS472 also
includes a common mode feedback loop that controls the output bias value to average it at
V_CC/2. This allows the device to always have a maximum output voltage swing, and by
consequence, maximize the input dynamic voltage range.
The advantages of a full-differential amplifier are:
● Very high PSRR (power supply rejection ratio).
● High common mode noise rejection.
● In theory, the filtering of the internal bias by an external bypass capacitor is not
necessary. But, to reach maximum performance in all tolerance situations, it is better to
keep this option.
5.2
Higher cut-off frequency
The higher cut-off frequency F_CH of the microphone preamplifier depends on the external
capacitors C₁, C₂.
TS472 has an internal first order low pass filter (R=40kΩ, C=100pF) to limit the highest cut-
off frequency on 40kHz (with a 3dB attenuation). By connecting C₁, C₂ you can decrease
F_CH by applying the following formula:
F_CH
=
----------------------------------------------¹-----------------------------------------------
2π ⋅ 40× 10³ ⋅ (C_{1, 2} + 100× 10^–12)
Figure 32 below indicates directly the higher cut-off frequency in Hz versus the value of the
output capacitors C₁, C₂ in nF.
Figure 32. Higher cut-off frequency vs. output
capacitors
40
10
1
200
400
600
800
1000
C1, C2 (pF)
For example, F_CH is almost 20kHz with C_1,2=100pF.
14/24