NE570 데이터 시트보기 (PDF) - ON Semiconductor
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NE570 Datasheet PDF : 10 Pages
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NE570
BASIC CIRCUIT HOOK−UP AND OPERATION
Figure 5 shows the block diagram of one half of the chip,
(there are two identical channels on the IC). The full−wave
averaging rectifier provides a gain control current, IG, for the
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.
THD_TRIM R3
INV. IN
DG_CELL_IN
R2
20 kW
3, 14
RECT_IN
R1
10 kW
2, 15
8, 9
DG
6, 11
R3
20 kW
5, 12
−
IG
30
R4
kW
VREF
1.8 V
+
1, 16
CRECT
7, 10
OUTPUT
VCC: PIN 13
GND: PIN 4
Figure 5. Chip Block Diagram (1 of 2 Channels)
The circuit is intended for use in single power supply
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 VREF. The non−inverting input of the op amp is tied
to VREF, and the summing nodes of the rectifier and DG cell
(located at the right of R1 and R2) have the same potential.
The THD_TRIM pin is also at the VREF potential.
Figure 6 shows how the circuit is hooked up to realize an
expander. The input signal, VIN, is applied to the inputs of
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 VOUT
will thus drop 12 dB, giving us the desired 2−to−1
expansion.
R3
*CIN1 R2
DG
−
VIN
*CIN2 R1
R4 VREF +
VOUT
Figure 7 shows the hook−up for a compressor. This is
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 RDC and
CDC. The values of RDC will determine the DC bias at the
output of the op amp. The output will bias to:
ǒ Ǔ VOUT DC +
1
)
RDC1
)
R4
RDC2
VREF
ǒ Ǔ VOUT DC +
1
)
RDC TOT
30 kW
1.8 V
The output of the expander will bias up to:
ǒ Ǔ VOUT DC +
1
)
R3
R4
VREF
ǒ Ǔ VOUT DC +
1
)
20
30
kW
kW
1.8 V + 3.0 V
The output will bias to 3.0 V when the internal resistors
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.
R2
DG
R1
*RDC
*CIN R3
VIN
−
R4 VREF +
*CRECT
*RDC
*CDC
*CF
VOUT
NOTES:
ǒ Ǔ GAIN =
R1 R2 IB 1
2 R3 VIN(avg.) 2
IB = 140 mA
* EXTERNAL COMPONENTS
Figure 7. Basic Compressor
NOTES:
2
2 R3 VIN (Avg.)
GAIN =
R1 R2 IB
IB = 140 mA
*CRECT
* EXTERNAL COMPONENTS
Figure 6. Basic Expander
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