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Ts742 microphone preamplifier

This low noise microphone preamplifier is based on TS472 chip manufactured by St Microelectronics.
The TS472 is a very low noise microphone preamplifier designed for PDA and notebook audio systems .
Main features of TS472 microphone preamplifier are : Low noise (10 nV/HZ),Differential input/output, 2.2 to 5.5 single supply ,Low power consumption , Low distortion ,Standby function ,ESD protection .

The TS472 can be used in applications like video and photo camera, sound acquisition and voice recognition applications, notebook and PDAs audio systems .
ts742 microphone preamplifier
External components description for TS472 application schematic .
Cin+, Cin- Input coupling capacitors .
Cout+, Cout- Output coupling capacitors
Rout+, Rout- Output load resistors used to charge the output coupling capacitors
Cout. Rpos, Rneg Polarizing resistors for biasing of a microphone.
Cs Supply bypass capacitor that provides power supply filtering.
Cb provides half-supply filtering.
C1, C2 Low pass filter capacitors allowing to cut the high frequency.
The higher cut-off frequency of the TS472 preamplifier depends on the external capacitors C1, C2.

TS472 has an internal first order low pass filter to limit the highest cutoff frequency on 40kHz.
Connecting C1, C2 we can decrease higher cut-off frequency applying the following formula:
For C1,2=100pF ,FCH is almost 20kHz .
ts742 microphone preamplifier circuit
The lower cut-off frequency FCL of the circuitdepends on the input capacitors Cin and output capacitors Cout.The input capacitors Cin in series with the input impedance of the TS472 (100k) are equivalent to a first order high pass filter.
 ts742 microphone preamplifier circuit
The capacitors Cout in series with the output resistors Rout (or an input impedance of the next stage) are also equivalent to a first order high pass filter.
ts742 microphone preamplifier
The gain of the TS472 microphone amplifier can be set from -1.5 dB to 41 dB by connecting an external grounded resistor RGS to the GS pin.
ts742 microphone preamplifier gain
For low noise applications the track layer from TS472 to C1, C2 and Rgs must be as short as is possible .

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