msm7503 Oki Semiconductor, msm7503 Datasheet - Page 6

• Manufacturer Part Number: msm7503
• Description: Multi-function Pcm Codec
• Manufacturer: Oki Semiconductor

¡ Semiconductor
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.
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).
Main amplifier gain without capacitors
A circuit example for adjustment of frequency characteristics
RPO
R1
C1
RMI
R2
C2
G=
RMO0
R2
R1
MSM7503
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