TSH512

General description

Doc ID 8120 Rev 7

19/31

Figure 26.

LNA schematics

The LNA gain is given by:

The high-pass cut-off frequency is:

The lowpass filter cut-off frequency is:

If you connect an external circuit to the LNA output, the impedance of this external circuit

should be higher than 10 m

Ωand the capacitance lower than 50 pF in order to keep a good

stability.

Note:

The capacitor C must be connected directly to input pin 12.

5.2

Electret condenser microphone source

When an electret condenser microphone (ECM) is used, a high gain LNA is recommended,

but low frequencies have to be attenuated. The ECM must be biased with a stable and clean

reference voltage. The TSH512 provides the LNA and the MIC-BIAS sections to perform this

function (see Section 5.3. MIC-BIAS section: microphone bias voltage).