msm7557 Oki Semiconductor, msm7557 Datasheet - Page 5

• Manufacturer Part Number: msm7557
• Description: Single Chip Msk Modem With Compandor For Cordless Telephone
• Manufacturer: Oki Semiconductor

¡ Semiconductor
(Continued)
Name
VR1
VR2
VR3
TVIO
TVI
CC1
CC2
CC3N
CC3P
Modulator output level control.
Refer to the following figure.
V
V
This level is made from internal voltage reference, so this level doesn't depend on power supply voltage.
Transmit side RC active filter input (TVI) and output (TVIO).
If over 50 kHz frequency element is in the input signal, folding noise is generated from internal SCF
circuit, so second order RC-active filter is needed. (fc = 10 kHz)
When digital "1" is applied to TVE pin, transmit voice signal comes out to TAO.
Capacitor connection pins to remove for DC offset of the compressor.
A 1 mF capacitor between SG pin and each pin should be connected.
Capacitor connection pins for the compressor attack and recovery time.
When DYN is digital "0" level, a 0.22 mF capacitor should be connected between CC3N and CC3P.
And when DYN is digital "1" level, a 0.47 mF capacitor should be connected between them.
TAO
TAO
= 20 ¥ log (R2/R1) – 9 dBV (DYN = "0" )
= 20 ¥ log (R2/R1) – 1 dBV (DYN = "1" )
C1
To transmit filter
R3
From modulator
C2
R5
R4
Example of fc = 10 kHz and 0 dB gain
C3
R3 = R4 = R5 = 68 k W
C1 = 0.22 mF, C2 = 510 pF, C3 = 110 pF
C19
Description
TVIO
TVI
CMPI
SG
–
+
–
+
–
+
Compressor
VR1
VR2
VR3
R5 ≥ 60 kW
C1 and C19 are used for DC cut.
VTVI
R1
R2
R1 ≥ 40 kW
R2 ≥ 40 kW
R1 ≥ R2
MSM7557
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