DA9191A.000
July 31, 1997
FUNCTIONS
The gain of GC4 can be adjusted in the range
-
examined at TAUDOUT with this switch. Also with
switch TXTST, the performance of GC8,
3.75..3.75dB., F12 and F15 can be observed with an
input at TAUDIN. An external capacitor between pins
TADOUT and TAUDIN is required. The TAUDIN
input is connected to switch S19. The switch can be
used to mute the TX audio block. S19 is controlled
with bit 5 in register 01HEX. Switch S19 is also
controlled by the TX framing block. During data
transmission on the voice channel and with the
AUMUT bit in register 13HEX set to high the TX audio
block is muted with S19. Following S19 is a second
order lowpass filter F13 with 15kHz cutoff frequency.
After filtering the signal is summed with the data
signal and amplified with GC9. The gain of the
amplifier GC9 is adjustable with bits 0..3 located in
register 0CHEX. The adjustment is done in 16 steps in
the range -3.0.. +3.0dB .The output of the amplifier
GC9 is then filtered with F14. The filter is a third
order lowpass filter with 54kHz cutoff frequency. The
gain at 1kHz is 0dB.
0.67..+5.33dB with bits 0..3 in register 0AHEX. After
GC4 the signal is filtered with pre-emphasis filter
F10, which has a +6dB/octave (±1dB) frequency
response at the range 300Hz..3kHz. At 1kHz the
gain is 0dB. The pre-emphasis filter can be bypassed
with switch S14.The signal is then amplified with
GC5. Gain control GC5 is an SC-type with a
programmable gain adjustment. The range is 0dB..-
20 dB with 16 steps according to bits 0..3 in register
0AHEX
.
At the output of GC5 is output pin LPFIN (or
highpass filter F9HP) and a SC-type limiter. The
limiting level is 439mVp and the tolerance is ±5%.
The 0dB level is 370mVp. The limiter can be
bypassed with switch S15. The lowpass filter F11
with a 6kHz notch follows the limiter. The gain of the
filter is 2.94dB at 1kHz. The filter and the limiter can
be bypassed with switch S16. GC6 and GC7 are
continuous time programmable gain adjustment
blocks. The gain of GC6 is -3dB ... +3dB with 16
step according to bits 0..3 in register 0BHEX. The gain
of GC7 is adjustable within - 3dB ... +1dB with bits
0..3 in register 0BHEX in 16 steps.
DTX bit of the regiter 0DHEX is used to set DATA,
DSAT and DST deviation. When the device is not in
DTX (Discontinous Transmission) the DTX = 0 and
there is nominal level at TX, 93 mVrms. If DTX is on,
GC7 output is connected to pin TAUDOUT through
switch TXTST. The data transmission signal can be
the level is increased to 373 mVrms.
20
MAS [ MICRO ANALOG SYSTEMS ]
