SA571 PHILIPS [NXP Semiconductors], SA571 Datasheet - Page 8

• Manufacturer Part Number: SA571
• Description: Compandor
• Manufacturer: PHILIPS [NXP Semiconductors]

output signal. The distortion trim is effective in nulling out any control
current source to the G input pin. This effectively trims I
Philips Semiconductors
Control signal feedthrough is generated in the gain cell by imperfect
device matching and mismatches in the current sources, I
When no input signal is present, changing I
signal feedthrough, but in general, the null for minimum feedthrough
will be different than the null in distortion. The control signal
feedthrough can be trimmed independently of distortion by tying a
shows such a trim network.
OPERATIONAL AMPLIFIER
The main op amp shown in the chip block diagram is equivalent to a
741 with a 1MHz bandwidth. Figure 18 shows the basic circuit. Split
collectors are used in the input pair to reduce g
compensation capacitor of just 10pF may be used. The output
stage, although capable of output currents in excess of 20mA, is
biased for a low quiescent current to conserve power. When driving
heavy loads, this leads to a small amount of crossover distortion.
1997 Aug 14
Compandor
–100
–IN
Figure 17. Control Signal Feedthrough
+20
–20
–40
–60
–80
0
–40
Figure 18. Operational Amplifier
100k
Q
3
Figure 16. Dynamic Range
Q
V
1
110dB
CC
3.6V
R-SELECT FOR
I
1
Q
VCA GAIN (0dB)
470k
2
Q
–20
4
SIGNAL LEVEL
+IN
C
MAXIMUM
C
TO PIN 3 OR 14
Q
D
D
2
I
G
2
1
2
0
will cause a small
20kHz BW
NOISE IN
M
, so that a small
Q
90dB
6
OUT
1
. Figure 17
1
SR00690
and I
SR00691
SR00692
2
.
8
Inspection of the gain equations in Figures 7 and 8 will show that the
external resistors, the internal resistor accuracy and tempco become
RESISTORS
basic compressor and expander circuit gains may be set entirely by
resistor ratios and the internal voltage reference. Thus, any form of
resistors that match well would suffice for these simple hook-ups,
and absolute accuracy and temperature coefficient would be of no
importance. However, as one starts to modify the gain equation with
very significant. Figure 19 shows the effects of temperature on the
diffused resistors which are normally used in integrated circuits, and
the ion-implanted resistors which are used in this circuit. Over the
critical 0 C to +70 C temperature range, there is a 10-to-1 improve-
ment in drift from a 5% change for the diffused resistors, to a 0.5%
change for the implemented resistors. The implanted resistors have
another advantage in that they can be made the size of the diffused
resistors due to the higher resistivity. This saves a significant
amount of chip area.
Figure 19. Resistance vs Temperature
1.15
1.10
1.05
1.00
.95
Ç Ç Ç Ç Ç Ç
Ç Ç Ç Ç Ç Ç
–40
TEMPERATURE
0
40
80
120
140 /
1 % ERROR
1k /
DIFFUSED
RESISTOR
LOW TC
IMPLANTED
RESISTOR
Product specification
BAND
SA571
SR00693