Regulator; Audio Pre-Amplifier; Audio Power Amplifier - Motorola XTS 2500 Service Manual

VHF Detailed Theories of Operation: VOCON Functional Blocks
4.1.6.2.1.3 Audio Circuitry
A16-bit CODEC is integrated into the MAKO IC and programmable by the dual-core processor
through the SPI bus. The CODEC converts microphone audio data into a digital bit stream for
processor by the DSP and converts receive audio data that was processed by the DSP into an
analog audio signal for amplification to a speaker. The CODEC interfaces to the DSP through the
4-wire SAP bus. The CODEC clock, which is 512kHz, is generated by the MAKO IC and supplied on
the VC_DCLK pin (R772). The CODEC 8 kHz frame synchronization signal is generated by the
MAKO IC and supplied on the VC_FSYNC pin (R773). The CODEC transmit data signal is on the
VC_TX3V pin and the CODEC receive data signal is on the VC_RX pin. For the MAKO IC to
generate the clock and frame sync signals, a 24.576 MHz crystal Y702 is supplied to the XOUT and
XIN pins.
The MAKO IC contains internal amplification (digital and analog), filtering, and multiplexing
functionality for both receive and transmit audio. These functions are programmable by the dual core
processor through the SPI bus. The input for the internal microphone audio (C755) is the
INT_MIC_P pin, while the input for the external microphone audio (C754) is the EXT_MIC_P pin.
The differential output for the internal speaker is the INT_SPKR_P pin and INT_SPKR_M pin. The
differential output for the external speaker is the EXT_SPKR_P pin (C769) and EXT_SPKR_M pin
(C768).

4.1.6.2.2 Regulator

The 5 V regulator is internal to the MAKO IC and uses SW_B+ as its input voltage at pin V08_I
(C720). The 5 V supply (L705) is used by the bi-directional voltage translators integrated into the
MAKO IC, the MAKO IC protection diodes, and the ESD protection circuitry.
The 1.55 V regulator (programmable through the SPI bus) is integrated into the MAKO IC. This
regulator uses VSW2 to source the current. The 1.55 V supply (R718) is used by the dual-core
processor U701 for it core voltage and clock amplifier.

4.1.6.2.3 Audio Pre-Amplifier

The audio pre-amplifier is integrated into the MAKO IC. The pre-amplifier's supply voltage and gain
are programmable and controlled by the dual-core processor through the SPI bus. The input to the
pre-amplifier is routed from the internal gain stages within the MAKO IC. The differential output of the
pre-amplifier is the VC_OUT_P pin (R844) and VC_OUT_M pin (R798).

4.1.6.2.4 Audio Power Amplifier

The audio power amplifier, supplied by SW_B+, is integrated into the MAKO IC U701. The audio PA
is a programmable BTL type and is controlled by the dual-core processor through the SPI bus. The
operational state of the PA, as well as selecting between the internal and external audio path, is
controlled by the dual-core processor via the SPI bus.
The differential input to the audio PA comes from a low-pass filter (R844, R798, C764, C765, and
C790) at the output of the audio pre-amplifier.
6816985H01-F
4.1-11
February 14, 2012