MSM7503 Просмотр технического описания (PDF) - Oki Electric Industry

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MSM7503

Multi-Function PCM CODEC

Oki Electric Industry 

¡ Semiconductor

MSM7503

RMI, RMO0, RMO1

Receive main amplifier input and outputs.

RMI is the inverted input and RMO0 and RMO1 are the outputs of the receive main amplifier.

The output signal on RMO1 is inverted against RMO0 by a gain 1 (0 dB), so the earphone of a

handset is directly connected between RMO0 and RMO1. During the system power down, the

RMO0 and RMO1 outputs are in a high impedance state. The receive main amplifier gain is

determined by a resistor connected between RPO and RMI, and a resistor connected between

RMI and RMO0. The receive main amplifier gain varies between 0 and +20 dB in effect. A piezo-

receiver with an impedance greater than 1.2 kW is available.

If the adjusting of receive path frequency characteristics is required, insert the following circuit

for adjustment. During the whole system Power ON, the speech path from RMI to RMO0 and

RMO1 is disconnected and the output of RMO0 and RMO1 is at the SG level (VA/2). The speech

path is provided by processor control.

A circuit example for adjustment of frequency characteristics

RPO

R1

RMI

C1

RMO0

R2

C2

Main amplifier gain without capacitors

G=

R2

R1

SPI

Addition input of speaker amplifier.

The typical gain between SPI and SPO is 0 dB. But, the 2-stage gain amplifier allows to set up a

gain between 0 dB and –18 dB in a 6 dB step, or a gain between 0 dB and –28 dB in a 4 dB step

through processor control. The input resistance of SPI is typically 20 kW to 150 kW (it varies by

gain setting).

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