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參數(shù)資料
| 型號(hào)： | MC33111 |
| 廠商： | Motorola, Inc. |
| 英文描述： | Low Voltage Compander |
| 中文描述： | 低電壓擴(kuò)展器 |
| 文件頁數(shù)： | 8/12頁 |
| 文件大?。?/td> | 131K |
| 代理商： | MC33111 |
MOTOROLA
8
MC33111
FUNCTIONAL DESCRIPTION
Introduction
The MC33111 compander (COMpressor and exPANDER)
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 temperature compensated references
required for accurate and stable performance.
Both the compressor and expander can be muted
independently 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 provided which sets both sections to unity
gain, regardless of input level.
Two uncommitted op amps are provided which can be
used for perpherial functions. Each is internally biased at Vb
(
≈
+1.5 V), and has a bandwidth of
≈
300 kHz.
NOTE
: All dB values mentioned in this data sheet, unless
otherwise noted, are referenced to 100 mVrms.
40 k
Output
2
7.5 k
Gain
Rectifier
ICONTROL
Iref
5
Vb
10 k
VCC
3
Input
1.0
μ
F
Figure 15. Compressor
Compressor
The compressor is a noninverting amplifier with a fixed
input resistor and a variable gain cell in its feedback path as
shown in Figure 15.
The amplifier output is sampled by the precision rectifier
which, in turn, supplies a DC signal (ICONTROL), representa-
tive of the rectifier’s AC signal, to the variable gain cell. The
reference current (IREF) 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
ICONTROL increases, thereby providing compression. The
output is related to the input by the following equation
(Vin and Vout are rms volts):
Vout
(1)
In terms of dB levels, the relationship is:
Vo(dB) = 0.5 x Vi(dB)
where 0 dB = 100 mVrms (See Figures 3 and 4).
The input and output are internally biased at Vb (
≈
+1.5 V),
and must therefore be capacitor coupled to external circuitry.
Pin 3 input impedance is nominally 10 k
(
±
20%), and the
maximum functional input signal is listed in the Recommended
(2)
0.3162 x
Vin
Operating Conditions table. Bias currents required by the op
amp and the variable gain cell are internally supplied. Due to
clamp diodes at the input (to VCC and ground), the input signal
must be maintained between the supply rails. If the input signal
goes more than 0.5 V above VCC or below ground, excessive
currents will flow, and distortion will show up at the output and
possibly in other parts of the circuit.
When AC signals are not present at the input, the variable
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.
The output of the rectifier is filtered by the capacitor at
Pin 5, which, in conjunction with an internal 20 k resistor,
provides 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.
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