NE570 ON Semiconductor, NE570 Datasheet - Page 5

• Manufacturer Part Number: NE570
• Description: Compandor
• Manufacturer: ON Semiconductor

BASIC CIRCUIT 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
expander. The input signal, V
both the rectifier and the DG cell. When the input signal
drops by 6.0 dB, the gain control current will drop by a factor
of 2, and so the gain will drop 6 dB. The output level at V
will thus drop 12 dB, giving us the desired 2−to−1
expansion.
DG_CELL_IN
Figure 5 shows the block diagram of one half of the chip,
The circuit is intended for use in single power supply
Figure 6 shows how the circuit is hooked up to realize an
V
NOTES:
GAIN =
I
* EXTERNAL COMPONENTS
B
RECT_IN
IN
Figure 5. Chip Block Diagram (1 of 2 Channels)
REF
= 140 mA
, and the summing nodes of the rectifier and DG cell
REF
3, 14
2, 15
2 R
*C
*C
IN1
IN2
3
R
. The non−inverting input of the op amp is tied
R
20 kW
R
10 kW
1
V
2
1
Figure 6. Basic Expander
IN
R
R
R
2
(Avg.)
2
1
I
B
THD_TRIM
C
DG
RECT
2
1
DG
8, 9
1, 16
I
G
and R
30 kW
*C
R3
IN
RECT
R
6, 11
R
20 kW
4
, is applied to the inputs of
2
R
3
) have the same potential.
4
V
1.8 V
REF
INV. IN
V
REF
REF
5, 12
potential.
−
+
R
3
−
+
V
GND: PIN 4
CC
7, 10
OUTPUT
: PIN 13
G
, for the
http://onsemi.com
V
OUT
OUT
NE570
5
essentially an expander placed in the feedback loop of the op
amp. The DG cell is set−up to provide AC feedback only, so
a separate DC feedback loop is provided by the two R
C
output of the op amp. The output will bias to:
The output of the expander will bias up to:
are used. External resistors may be placed in series with R3,
(which will affect the gain), or in parallel with R4 to raise the
DC bias to any desired value.
DC
Figure 7 shows the hook−up for a compressor. This is
The output will bias to 3.0 V when the internal resistors
NOTES:
GAIN =
I
* EXTERNAL COMPONENTS
B
= 140 mA
. The values of R
V
V
IN
V
OUT
OUT
2 R 3 V IN (avg.)
*C
R 1 R 2 I B
V
DC +
DC +
Figure 7. Basic Compressor
V
IN
OUT
OUT
R
DC +
3
DC +
R
4
DC
1 ) 20 kW
1
2
1 )
V
will determine the DC bias at the
REF
*R
30 kW
1 )
DC
R
1 )
DC1
R
−
+
30 kW
DC TOT
DG
R
R
R
) R
1.8 V + 3.0 V
*C
*C
4
3
4
RECT
DC
V
DC2
*R
1.8 V
REF
R
R
DC
2
1
V
REF
*C
V
F
OUT
DC
and