ML33111
LANSDALE Semiconductor, Inc.
Power Supply
The ML33111 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.
LEGACY APPLICATIONS INFORMATION
Typical Application Circuit
Figure 18 indicates a typical implementation of the ML33111
compander. The following points apply:
a) The values shown adjacent to some components are based on
the expected use of the IC:
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 micro
phone amplifier is only an example.
—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.
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.
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.
f) The logic inputs (Pins 4, 8, 12) are TTL/CMOS compatible. The
logic high voltage must not exceed the V voltage on the
CC
ML33111. Any unused input should be connected to ground
and not left open.
Figure 18. Typical Application
20 k
ML33111
0.47
14
11
15 k
Expander
Input
15
2
Expander
Output
∆
Gain
40 k
Vb
1.0
µF
Rectifier
Compressor
Input
10 k
3
5
Compressor
Output
Vb
Gain
0.47
7.5 k
16
1
V
∆
CC
Bias &
Reference
Generator
4.7/
0.01
1.0 µF
40 k
Rectifier
V+
10
9
4
CM
Mute/
Passthrough
Logic
µ
P or
12 EM
8 PT
Vb
Other Control Circuit
Microphone
Vb
7
6
(See Text For Component Values)
Signal-To-Noise Improvement
Among the basic reasons for the original development of compan-
der type circuits was to improve the signal-to-noise ratio of long dis-
tance communications circuits, and of voice circuits which are trans-
mitted 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 its
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 trans-
mitter and receiver. The ML33111 was designed for a two-to-one
compression and expansion, i.e. a 60 dB dynamic signal is com-
pressed to a 30 dB dynamic range, transmitted to the receiving end,
and then expanded back to a 60 dB dynamic range.
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