MC33111 Datasheet, PDF (10/12 Pages) Motorola, Inc – Low Voltage Compander

Power Supply
The MC33111 requires a supply voltage between 3.0 V
and 7.0 V, and a nominal current of ≈ 1.6 mA. The supply
voltage should be well filtered and free of ripple. A minimum
of 4.7 µF in parallel with a 0.01 µF capacitor is recommended
for filtering and RF bypass.
Vb is an internally generated reference set at ≈ +1.5 V, and
is used internally as an AC ground. It is not available directly
at any pins, but can be obtained as a buffered reference from
either op amp by connecting the op amp as a follower.
APPLICATION INFORMATION
Typical Application Circuit
Figure 18 indicates a typical implementation of the
MC33111 compander. The following points apply:
a) The values shown adjacent to some components are
based on the expected use of the IC:
— The input capacitors (Pins 3 and 14) provide a 3.0 dB
rolloff of ≈ 30 Hz, a decade below the nominal
voiceband.
— The rectifier capacitors provide attack and decay times
as indicated in the Electrical Tables.
b) The values for the unlabeled components are application
dependent:
— The components around the op amps depend on their
use.
— The value of the capacitors at the compressor and
expander outputs depend on the circuit to which they
are connected.
c) If either the compressor or expander is not used, its input
must not be left open. It can be connected to ground
either through a capacitor, or directly to ground.
d) The two op amps can be used for any purpose which suits
the application. The indicated use of the one op amp as a
microphone amplifier is only an example.
e) If an op amp is not used, its output and input must be
connected together. Do not leave Pin 7 or Pin 9 open.
f) The logic inputs (Pins 4, 8, 12) are TTL/CMOS compatible.
The logic high voltage must not exceed the VCC voltage on
the MC33111. Any unused input should be connected to
ground and not left open.
Figure 18. Typical Application
Microphone
MC33111
Expander ^{0.47 14}
Input
11
1.0 µF
40 k
Compressor
Input
3
0.47
10 k
Vb
5
1.0 µF
V+
10
∆ Gain
Rectifier
9 ^Vb
Vb
7
15 k
∆ Gain
Rectifier
20 k
Vb
7.5 k
Bias &
40 k
Reference
Generator
15
Expander
Output
2
Compressor
Output
16
4.7/
VCC
1
0.01
Mute/
Passthrough
Logic
4 CM
12 EM
8 PT
µP or
Other Control Circuit
6
(See Text For Component Values)
Signal-To-Noise Improvement
Among the basic reasons for the original development of
compander type circuits was to improve the signal-to-noise
ratio of long distance communications circuits, and of voice
circuits which are transmitted over RF links (CBs,
walkie-talkies, cordless phones, etc.). Since much of the
interfering noise heard at the receiving end of a transmission
is due to noise picked up, for example, in the airway portion of
the RF link, the compressor was developed to increase the
low-level signals at the transmitting end. Then any noise
picked up in the RF link would be a smaller percentage of the
transmitted signal level. At the receiving end, the signal is
then expanded back to is original level, retaining the same
high signal-to-noise ratio. While the above explanation
indicates it is not necessary to attenuate strong signals (at
the transmitting end), a benefit of doing this is the reduced
dynamic range which must be handled by the system
transmitter and receiver. The MC33111 was designed for a
two-to-one compression and expansion, i.e. a 60 dB dynamic
signal is compressed to a 30 dB dynamic range, transmitted
to the receiving end, and then expanded back to a 60 dB
dynamic range.
MOTOROLA
10
MC33111