ncy9100 ON Semiconductor, ncy9100 Datasheet - Page 5

• Manufacturer Part Number: ncy9100
• Description: Compandor
• Manufacturer: ON Semiconductor

electronic
applications,
transconductance amplifier can be used, but when
high−performance is required, one has to resort to complex
discrete circuitry with many expensive, well−matched
components. This paper describes an inexpensive integrated
circuit, the NCY9100 Compandor, which offers a pair of
high performance gain control circuits featuring low
distortion (<0.1%), high signal−to−noise ratio (90 dB), and
wide dynamic range (110 dB).
Circuit Background
satisfy the requirements of the telephone system. When
several telephone channels are multiplexed onto a common
line, the resulting signal−to−noise ratio is poor and
companding is used to allow a wider dynamic range to be
passed through the channel. Figure 4 graphically shows
what a compandor can do for the signal−to−noise ratio of a
restricted dynamic range channel. The input level range of
+20 to −80 dB is shown undergoing a 2−to−1 compression
where a 2.0 dB input level change is compressed into a
1.0 dB output level change by the compressor. The original
100 dB of dynamic range is thus compressed to a 50 dB
range for transmission through a restricted dynamic range
channel. A complementary expansion on the receiving end
restores the original signal levels and reduces the channel
noise by as much as 45 dB.
the rectifier and the gain control element. The phone system
Much interest has been expressed in high performance
The NCY9100 Compandor was originally designed to
The significant circuits in a compressor or expander are
Figure 4. Restricted Dynamic Range Channel
INPUT
LEVEL
+20
0dB
−40
−80
gain
an
INTRODUCTION
control
integrated
NOISE
circuits.
circuit
For
OUTPUT
LEVEL
0dB
non−critical
−20
−40
−80
operational
http://onsemi.com
5
requires a simple full−wave averaging rectifier with good
accuracy, since the rectifier accuracy determines the (input)
output level tracking accuracy. The gain cell determines the
distortion and noise characteristics, and the phone system
specifications here are very loose. These specs could have
been met with a simple Operational Transconductance
Multiplier, or OTA, but the gain of an OTA is proportional
to temperature and this is very undesirable. Therefore, a
linearized transconductance multiplier was designed which
is insensitive to temperature and offers low noise and low
distortion performance. These features make the circuit
useful in audio and data systems as well as in
telecommunications systems.
Basic Hook−up and Operation
(there are two identical channels on the IC). The full−wave
averaging rectifier provides a gain control current, I
variable gain (DG) cell. The output of the DG cell is a current
which is fed to the summing node of the operational
amplifier. Resistors are provided to establish circuit gain and
set the output DC bias.
systems, so the internal summing nodes must be biased at
some voltage above ground. An internal band gap voltage
reference provides a very stable, low noise 1.8 V reference
denoted V
to V
(located at the right of R
The THD trim pin is also at the V
Figure 5 shows the block diagram of one half of the chip,
The circuit is intended for use in single power supply
RECT
REF
Figure 5. Chip Block Diagram (1 of 2 Channels)
G
3,14
2,15
IN
, and the summing nodes of the rectifier and DG cell
IN
REF
20kW
10kW
R
R
. The non−inverting input of the op amp is tied
THD TRIM
2
1
C
DG
RECT
IG
1,16
8,9
1
20kW
and R
R
30kW
3
R
R
3
4
2
6,11
) have the same potential.
REF
INV
V
1.8V
IN
REF
potential.
5,12
V
GND PIN 4
CC
−
+
PIN 13
OUTPUT
G
7,10
, for the