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¡ Semiconductor

MSM7575

Voice Input

GSX2

VOXO

VOXI

Voice Output

VFRO

Presence

Detect

Absence

Detect (Hang-over time)

Normal Voice Signal

Decoded Time period

Background

Noise

(a) Transmit VOX Function Timing Diagram

(b) Receive VOX Function (CR6-B3: digital "0") Timing Diagram

(Presence)

(Presence)

(Presence)

(Absence)

(Absence)

(Presence)

Note: VOXO, VOXI function become valid when setting CR6-B7 to digital “1”.

Figure 4 VOX Function

VOXO

Transmit VOX function signal output.

VOX function is to recognize the presence or absence of the transmit voice signal by detecting the

signal energy. “H” and “L” levels set to this pin correspond to the presence and the absence,

respectively. This result appears also at the register data CR7-B7. The signal energy detect

threshold is set by the control register data CR6-B6, B5.

VOXI

Signal input for receive VOX function.

The “H” level at VOXI indicates the presence of voice signal, the decoder block processes normal

receive signal, and the voice signal appears at analog output pins . The “L” level indicates the

absence of voice signal, the background noise generated in this device is transferred to the analog

output pins. The background noise amplitude is set by the control register CR6. Because this

signal is ORed with the register data CR6-B3, the control register data CR6-B3 should be set to

digital “0”.