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BTM52 DATASHEET

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5.3.8

Audio Input Stage

The audio input stage of the module consists of a low noise input amplifier, which receives

its analogue input signal from pins MIC_A_P and MIC_A_N to a second–order ∑-∆ ADC

that outputs a 4Mbit/sec single-bit stream into the digital circuitry. The input can be

configured to be either single ended or fully differential. It can be programmed for either

microphone or line input and has a 3-bit digital gain setting of the input-amplifier in 3dB

steps to optimize it for the use of different microphones.

5.3.9

Microphone Input

5.3.10

Audio Output Stage

The output digital circuitry converts the signal from 16-bit per sample, linear PCM of

variable sampling frequency to a 2Mbits/sec multi-bit stream, which is fed into the analogue

output circuitry.

The output circuit comprises a digital to analogue converter with gain setting and output

amplifier.Its class-AB output-stage is capable of driving a signal on both channels of up to

2V

pk-pk- differential into a load of 16 . The output is available as a differential signal

between SPK_A_P and SPK_A_N for the left channel; and between SPK_B_P and

SPK_B_N for the right channel. The output is capable of driving a speaker directly if its

impedance is at least 8

if only one channel is connected or an external regulator is used.

The gain of the output stage is controlled by a 3-bit programmable resistive divider, which

sets the gain in steps of approximately 3dB.

The multi-bit stream from the digital circuitry is low pass filtered by a second order

bi-quad filter with a pole at 20kHz. The signal is then amplified in the fully differential

output stage, which has a gain bandwidth of typically 1MHz.

5.3.11

PCM

The audio pulse code modulation (PCM) interface supports continuous transmission and

reception of PCM encoded audio data over Bluetooth.

Pulse Code Modulation (PCM) is a standard method used to digitize audio (particularly

voice) for transmission over digital communication channels.Through its PCM interface,

BTM52

provide hardware support for continual transmission and reception of PCM

data, thus reducing processor overhead for wireless headset applications.BTM52offers a

bi-directional digital audio interface that routes directly into the baseband layer of the

on-chip firmware. It does not pass through the HCI protocol layer.