SA572 Datasheet, PDF (4/12 Pages) NXP Semiconductors – Programmable analog compandor

Philips Semiconductors
Programmable analog compandor
Product specification
SA572
TEST CIRCUIT
2.2µF
V₁
(7,9) 6.8k
∆G
5Ω
= 10µF
(2,14)
(4,12)
BUFFER
(5,11)
82k
1%
R₃
17.3k
1µF
100Ω
22µF
+
–15V
–
270pF
NE5234
2.2k
V₀
(6,10)
+
1k
+
2.2µF
(8)
(1,15)
2.2µF _{3.3k (3,13)}
V₂
R₂
1%
RECTIFIER
(16)
Figure 3. Test Circuit
.1µF
+
22µF
+15V
SR00696
AUDIO SIGNAL PROCESSING IC COMBINES VCA
AND FAST ATTACK/SLOW RECOVERY LEVEL
SENSOR
In high-performance audio gain control applications, it is desirable to
independently control the attack and recovery time of the gain
control signal. This is true, for example, in compandor applications
for noise reduction. In high end systems the input signal is usually
split into two or more frequency bands to optimize the dynamic
behavior for each band. This reduces low frequency distortion due
to control signal ripple, phase distortion, high frequency channel
overload and noise modulation. Because of the expense in
hardware, multiple band signal processing up to now was limited to
professional audio applications.
With the introduction of the Signetics SA572 this high-performance
noise reduction concept becomes feasible for consumer hi fi
applications. The SA572 is a dual channel gain control IC. Each
channel has a linearized, temperature-compensated gain cell and an
improved level sensor. In conjunction with an external low noise op
amp for current-to-voltage conversion, the VCA features low
distortion, low noise and wide dynamic range.
The novel level sensor which provides gain control current for the
VCA gives lower gain control ripple and independent control of fast
attack, slow recovery dynamic response. An attack capacitor C_A
with an internal 10k resistor R_A defines the attack time t_A. The
recovery time t_R of a tone burst is defined by a recovery capacitor
C_R and an internal 10k resistor R_R. Typical attack time of 4ms for
the high-frequency spectrum and 40ms for the low frequency band
can be obtained with 0.1µF and 1.0µF attack capacitors,
respectively. Recovery time of 200ms can be obtained with a 4.7µF
recovery capacitor for a 100Hz signal, the third harmonic distortion
is improved by more than 10dB over the simple RC ripple filter with
a single 1.0µF attack and recovery capacitor, while the attack time
remains the same.
The SA572 is assembled in a standard 16-pin dual in-line plastic
package and in oversized SOL package. It operates over a wide
supply range from 6V to 22V. Supply current is less than 6mA. The
SA572 is designed for applications from –40°C to +85°C.
1998 Nov 03
4