mc33111p Lansdale Semiconductor, Inc., mc33111p Datasheet - Page 8

• Manufacturer Part Number: mc33111p
• Description: Low Voltage Compander
• Manufacturer: Lansdale Semiconductor, Inc.

ML33111
Page 8 of 12
Introduction
is composed of two variable gain circuits which provide
compression and expansion of a signal’s dynamic range. The
compressor will take a signal with a 60 dB dynamic range
(1.0 mV to 1.0 Vrms), and reduce that to a 30 dB dynamic
range (10 mV to 316 mV) by attenuating strong signals,
while amplifying low level signals. The expander does the
opposite in that the 30 dB signal range is increased to a
dynamic range of 60 dB by amplifying strong signals and
attenuating low level signals. The 0 dB level is internally set
at 100 mVrms — that is the signal level which is neither
amplified nor attenuated. Both circuits contain the necessary
precision full wave rectifier, variable gain cell, and tempera-
ture compensated references required for accurate and stable
performance.
Compressor
input resistor and a variable gain cell in its feedback path as
shown in Figure 15.
which, in turn, supplies a DC signal (I CONTROL ), repre-
sentative of the rectifier’s AC signal, to the variable gain
cell. The reference current (I REF ) is an internally generated
precision current. The effective impedance of the variable
gain cell varies with the ratio of the two currents, and
decreases as I CONTROL increases, thereby providing com-
pression. The output is related to the input by the following
equation (V in and V out are rms volts):
and must therefore be capacitor coupled to external circuitry.
Pin 3 input impedance is nominally 10 kΩ (±20%), and the
The ML33111 compander (COMpressor and exPANDER)
The compressor is a noninverting amplifier with a fixed
The amplifier output is sampled by the precision rectifier
The input and output are internally biased at Vb (≈ +1.5 V),
where 0 dB = 100 mVrms (See Figures 3 and 4).
In terms of dB levels, the relationship is:
V out
Vo(dB) = 0.5 x Vi(dB)
0.3162 x V
in
Input
1.0 µF
3
5
V CC
FUNCTIONAL DESCRIPTION
10 k
I ref
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(1)
(2)
Figure 15. Compressor
Vb
ently by the use of Pins 4 and 12, respectively. A minimum
of 55 dB of muting is guaranteed for the compressor, and 60
dB for the expander. A passthrough function (Pin 8) is pro-
vided which sets both sections to unity gain, regardless of
input level.
for perpherial functions. Each is internally biased at Vb
(≈ +1.5 V), and has a bandwidth of ≈300 kHz.
otherwise noted, are referenced to 100 mVrms.
maximum functional input signal is listed in the
Recommended Operating Conditions table. Bias currents
required by the op amp and the variable gain cell are inter-
nally supplied. Due to clamp diodes at the input (to V CC and
ground), the input signal must be maintained between the
supply rails. If the input signal goes more than 0.5 V above
V CC or below ground, excessive currents will flow, and dis-
tortion will show up at the output and possibly in other parts
of the circuit.
gain cell will attempt to set a very high gain to comply with
Equation 2. An internal clamp limits the maximum gain to
≈26 dB to prevent instabilities.
5, which, in conjunction with an internal 20 k resistor, pro-
vides the time constant for the attack and decay times.The
attack and decay times listed in the Electrical Characteristics
were determined using the test procedure defined in EIA-553.
Figure 9 indicates how the times vary with the capacitor value.
If the attack and decay times are decreased using a smaller
capacitor, performance at low frequencies will degrade.
I CONTROL
∆ Gain
Both the compressor and expander can be muted independ-
Two uncommitted op amps are provided which can be used
NOTE: All dB values mentioned in this data sheet, unless
Rectifier
When AC signals are not present at the input, the variable
The output of the rectifier is filtered by the capacitor at Pin
7.5 k
40 k
2
Output
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Issue A