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BTM8670 DATASHEET

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4.2.13

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_R_RP and SPK_R_RN for the left channel; and between SPK_L_LP and

SPK_L_LN 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.

4.3

PCM Interface

The audio PCM interface on the BTM8670 supports:

On-chip routing to Kalimba DSP

Continuous transmission and reception of PCM encoded audio data over

Bluetooth.

Processor overhead reduction through hardware support for continual

transmission and reception of PCM data

A bidirectional digital audio interface that routes directly into the baseband

layer of the firmware .It does not pass through the HCI protocol layer.

Hardware on the BTM8670 for sending data to and from a SCO connection.

Up to 3 SCO connections on the PCM interface at any one time.

PCM interface master, generating PCM_SYNC and PCM_CLK.

PCM interface slave, accepting externally generated PCM_SYNC and

PCM_CLK.

Various clock formats including:

Long Frame Sync

Short Frame Sync

GCI timing environments

13-bit or 16-bit linear, 8-bit u-law or A-law compander sample formats.

Receives and transmits on any selection of 3 the first 4 slots following

PCM_SYNC.

The PCM configuration options are enabled by setting the PS Key

PSKEY_PCM_CONFIG32.