SA572N ON Semiconductor, SA572N Datasheet - Page 6

• Manufacturer Part Number: SA572N
• Description: IC COMPANDOR 2CHAN GAIN 16-DIP
• Manufacturer: ON Semiconductor
• Type: Compandorr

Specifications of SA572N

• Applications: Automatic Level Control, Stereo Expander
• Mounting Type: Through Hole
• Package / Case: 16-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Philips Semiconductors
Rectifier
The rectifier is a full-wave design as shown in Figure 5. The input
voltage is converted to current through the input resistor R
turns on either Q
of the voltage to current converter is reduced by the loop gain of the
gain block A
from input bias current of gain block A
typically about 70nA. Frequency response of the gain block A
causes second-order error at high frequency. The collector current
of Q
wave rectified output current I
I
If V
I
The internal bias scheme limits the maximum output current I
around 300 A. Within a 1dB error band the input range of the rectifier
is about 52dB.
1998 Nov 03
R
RAC
Programmable analog compandor
V
IN
V
REF
6
IN
is mirrored and summed at the collector of Q
is AC-coupled, then the equation will be reduced to:
V
IN
V
IN
R
2
(AVG)
R
Figure 5. Simplified Rectifier Schematic
. If AC coupling is used, the rectifier error comes only
2
2
V
R2
REF
5
or Q
+
–
A2
6
depending on the signal polarity. Deadband
R
. The rectifier transfer function is
Q6
2
Q5
. The input bias current is
(4)
V+
5
I R
SR00698
to form the full
D7
V IN
2
and
R 2
2
R
V REF
also
to be
6
Buffer Amplifier
In audio systems, it is desirable to have fast attack time and slow
recovery time for a tone burst input. The fast attack time reduces
transient channel overload but also causes low-frequency ripple
distortion. The low-frequency ripple distortion can be improved with
the slow recovery time. If different attack times are implemented in
corresponding frequency spectrums in a split band audio system,
high quality performance can be achieved. The buffer amplifier is
designed to make this feature available with minimum external
components. Referring to Figure 6, the rectifier output current is
mirrored into the input and output of the unipolar buffer amplifier A
through Q
accuracy and provide common-mode bias for A
positive-going input signal, the buffer amplifier acts like a
voltage-follower. Therefore, the output impedance of A
contribution of capacitor CR to attack time insignificant. Neglecting
diode impedance, the gain Ga(t) for G can be expressed as
follows:
where
resistor. Diode D
negative-going signal if the value of capacitor CR is larger than
capacitor CA. The recovery time depends only on CR R
diode impedance is assumed negligible, the dynamic gain G
where R is the recovery time constant and R
resistor. The gain control current is mirrored to the gain cell through
Q
can be trimmed through the tracking trim pin into A
source of 3 A.
G is expressed as follows.
Ga(t)
14
G
Ga
Ga
G
A
R=R
R
. The low level gain errors due to input bias current of A
R
=R
(t)
INT
FNL
(t)=(G
A
A
R
=Initial Gain
=Final Gain
is the attack time constant and R
8
, Q
CA=10k CA
R INT
CR=10k CR
(Ga
(G
9
RINT
INT
and Q
–G
15
R FNL
opens the feedback loop of A
10
Ga
G
. Diodes D
) e +G
RFNL
FNL
e
e
R FNL
A
R
t
t
11
and D
Ga
G
RFNL
FNL
A
12
is a 10k internal
R
improve tracking
3
is a 10k internal
Product specification
. For a
3
for a
3
with a current
SA572
3
makes the
R
. If the
2
R
and A
(t) for
3
3