MC33411B Motorola, MC33411B Datasheet - Page 18

• Manufacturer Part Number: MC33411B
• Description: (MC33411A/B) ANALOG CORDLESS PHONE BASEBAND
• Manufacturer: Motorola

Transmit Speech Processing System
Out”. The gain of the microphone amplifier is set with external
resistors to receive the audio from the microphone hybrid or
any other audio source. The MCO output has rail–to–rail
capability. The ”Tx Audio” pin will be ac–coupled. The audio
transmit signal path includes automatic level control (ALC)
(also referred to as the Compressor), Tx mute, limiter, filters,
and Tx gain adjust. The ALC provides ”soft” limiting to the
output signal swing as the input voltage slowly increases.
With this technique the gain is slightly lowered to help reduce
distortion of the audio signal. The limiter section provides
hard limiting due to rapidly changing singal levels, or
transients. The ALC, TX mute, and limiter functions can be
enabled or disabled vis the MCU serial interface. The Tx gain
adjust can also be remotely controlled to set different desired
signal levels.
1.0 dB increments. It is controlled with bits 7/9–5 as shown in
Table 1. The effect of the gain setting under various
ALC/Limiter On/Off settings is shown in Figure 9.
capacitor filter with a corner frequency at 3.7 kHz. This
Gain Control
18
This portion of the audio path goes from ”Tx Audio” to ”Tx
The adjustable gain stage provides 20 levels of gain in
The Low–Pass Filter before the gain stage is a switched
Bit #9
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
–
Gain Control
Bit #8
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
–
Gain Control
Bit #7
Table 1. Tx Gain Adjust Programming (Register 7)
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
–
Gain Control
Bit #6
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
–
MC33411A/B
Gain Control
Bit #5
frequency is dependent upon the SCF clock, nominaly set to
165 kHz and is directly proportional to the SCF clock. The
filter response for inband, ripple, wideband, as well as phase
and group delay, are shown in Figures 10 through 14.
Bit 6/2 controls the mute. The limiter can be disabled by
programming a logic 1 into 6/5.
in Figure 15. The ALC gain is controlled by bits 6/11–12. If
both bits are programmed to a logic 0, the ALC gain is set to
5.0 dB. If bit 6/11 is set to a logic 1, the ALC gain will be set to
10 dB, whereas if bit 6/12 is set to a logic 1 the ALC gain will be
25 dB. The ALC function may be disabled by programming a
logic 1 into bit 6/6.
Programming this bit to a logic 0 sets the maximum gain to
23 dB. A lower maximum gain, nominally 13.5 dB, is
achieved by programming the bit to a logic 1. The entire
compressor can be bypassed (i.e., 0 dB) by programming bit
6/4 to a logic 1.
compressor, ALC, and limiter.
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
–
The mute switch at Pin 18 will mute a minimum of 60 dB.
The compressor with ALC transfer characteristic is shown
The compressor low maximum gain can be set with bit 6/8.
Figures 16 through 22 describe the characteristics of the
Gain
Ctl #
>25
<6
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
6
7
8
9
MOTOROLA RF/IF DEVICE DATA
Gain/Attenuation
Amount
–9.0 dB
–9.0 dB
–8.0 dB
–7.0 dB
–6.0 dB
–5.0 dB
–4.0 dB
–3.0 dB
–2.0 dB
–1.0 dB
1.0 dB
2.0 dB
3.0 dB
4.0 dB
5.0 dB
6.0 dB
7.0 dB
8.0 dB
9.0 dB
10 dB
10 dB
0 dB