Datasheet

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Functional Description

MC13783 Technical Data, Rev. 3.5

30 Freescale Semiconductor

4.3.4 Audio Input Section

4.3.4.1 Microphone Bias

Two microphone bias circuits are provided. One circuit supplies up to two handset microphones via the

two outputs MC1RB and MC1LB. The second circuit supplies the headset microphone via MC2B. The

microphone bias resistors of 2.2 kOhm are included. The bias circuits can be enabled and disabled.

The bias MC2B includes a microphone detect circuit which monitors the current flow through the output

both when the bias is disabled or enabled. This will generate an interrupt to the processor. In this way the

attach and removal of a headset microphone is detected. Also it allows to include a send/end series switch

with the microphone for signaling purposes. When the output of the MC2B gets out of regulation, an

interrupt is generated. This allows for connecting a switch in parallel to the microphone.

4.3.4.2 Microphone Amplifiers

Figure 8 on page 31 shows a block diagram of the microphone amplifier section. A selection can be made

between one of the three amplified inputs: the handset microphone connected to MC1RIN, the headset

microphone connected to MC2IN, and the line input TXIN. The selected channel can be fed into the

receive channel for test purposes. In addition a second amplified input channel can be selected for the

second handset microphone connected to MC1LIN. The gain towards to voice CODEC can be

programmed in 1 dB steps from –8 dB to +23 dB.

In addition to the microphone amplifier paths, there is also the possibility to route the stereo line in signal

from RXINR and RXINL to the voice CODEC dual ADC section. This allows for 13-bit, 16 kHz sampled

stereo recording of an analog source such as FM radio.

1000480001286144k 4 1536k

100164000644096k 2 2048k

101096000646144k 2 3072k

1011 to 1111 are reserved combinations

Table 16. MC1RB, MC1LB and MC2B Parametric Specifications

Parameter Condition Min Typ Max Units

Microphone Bias Internal Voltage MC1RB, MC1LB IL = 0

MC2B

2.23

2.00

2.38

2.10

2.53

2.20

Output Current Source only 0 — 500 µA

PSRR with respect to BP

20 Hz - 10 kHz

90 — — dB

Output Noise Includes REFA noise

CCITT psophometricly weighted

—1.53.0µVrms

Table 15. Stereo DAC Sample Rate Selection SPI Bits (continued)

SR3 SR2 SR1 SR0 FS N

MCL N

BCL