SA2531 A/B/C/E/G/U
or after pressing the MUTE key, the gain is reduced by > 60 dB.
Receive
The receive input is the differential signal of RI and STB. The gain of the receive path
is 2 dB (test circuit figure 5) with differential outputs, RO1/RO2 (0dB on 1000Ω versions).
When mute is active during dialling the gain is reduced by > 60dB. During DTMF dialling
a MF comfort tone is applied to the receiver. The comfort tone is the DTMF signal with
a level that is -30dB relative to the line signal.
The receive gain can be adjusted under user control by using the volume control keys (not
on SA2531D). The VOL key gives a 4dB increase or returns the gain to normal in a Toggle
Function. Alternatively the + and - keys may be used. The + key increases the gain to
a maximum of +6dB while the - key reduces the gain to a minimum of -4dB. Each press
of the keys changes the gain by approximately 2dB.
The gain is reset by the next on-hook.
Side Tone
Side Tone is controlled along with Return Loss by a Double Balance Bridge as shown in
Fig. 1.
Figure 1
Double balance bridge (return loss and side tone) with one common ground
A good side tone cancellation is achieved by using the following equation:
ZBAL =
ZLINE
R5
R1
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sames
SAMES [ SAMES ]
