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PDF SA572D Data sheet ( Hoja de datos )
| Número de pieza | SA572D | |
| Descripción | Programmable analog compandor | |
| Fabricantes | Philips | |
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INTEGRATED CIRCUITS
SA572
Programmable analog compandor
Product specification
IC17 Data Handbook
1998 Nov 03
Philips
Semiconductors
1 page  
Philips Semiconductors
Programmable analog compandor
Product specification
SA572
SA572 BASIC APPLICATIONS
Description
The SA572 consists of two linearized, temperature-compensated
gain cells (∆G), each with a full-wave rectifier and a buffer amplifier
as shown in the block diagram. The two channels share a 2.5V
common bias reference derived from the power supply but otherwise
operate independently. Because of inherent low distortion, low noise
and the capability to linearize large signals, a wide dynamic range
can be obtained. The buffer amplifiers are provided to permit control
of attack time and recovery time independent of each other.
Partitioned as shown in the block diagram, the IC allows flexibility in
the design of system levels that optimize DC shift, ripple distortion,
tracking accuracy and noise floor for a wide range of application
requirements.
Gain Cell
Figure 4 shows the circuit configuration of the gain cell. Bases of the
differential pairs Q1-Q2 and Q3-Q4 are both tied to the output and
inputs of OPA A1. The negative feedback through Q1 holds the VBE
of Q1-Q2 and the VBE of Q3-Q4 equal. The following relationship can
be derived from the transistor model equation in the forward active
region.
DVBEQ3Q4 + DBEQ1Q2
(VBE = VT IIN IC/IS)
ǒ Ǔ ǒ ǓVTIn
1
2
I
G
)
1
2
IO
IS
* VTIn
1
2
IG
*
1
2
IO
IS
where
IIN
+
VIN
R1
R1 = 6.8kΩ
I1 = 140µA
I2 = 280µA
ǒ Ǔ ǒ ǓVTIn
I1 ) IIN
IS
* VTIn
I2 * I1 * IIN
IS
(2)
where
IIN
+
VIN
R1
R1 = 6.8kΩ
I1 = 140µA
I2 = 280µA
IO is the differential output current of the gain cell and IG is the gain
control current of the gain cell.
If all transistors Q1 through Q4 are of the same size, equation (2)
can be simplified to:
IO
+
2
I2
@
IIN
@
IG
*
1
I2
ǒI2
*
2I1Ǔ
@
IG
(3)
The first term of Equation 3 shows the multiplier relationship of a
linearized two quadrant transconductance amplifier. The second
term is the gain control feedthrough due to the mismatch of devices.
In the design, this has been minimized by large matched devices
and careful layout. Offset voltage is caused by the device mismatch
and it leads to even harmonic distortion. The offset voltage can be
trimmed out by feeding a current source within ±25µA into the THD
trim pin.
The residual distortion is third harmonic distortion and is caused by
gain control ripple. In a compandor system, available control of fast
attack and slow recovery improve ripple distortion significantly. At
the unity gain level of 100mV, the gain cell gives THD (total harmonic
distortion) of 0.17% typ. Output noise with no input signals is only
6µV in the audio spectrum (10Hz-20kHz). The output current IO
must feed the virtual ground input of an operational amplifier with a
resistor from output to inverting input. The non-inverting input of the
operational amplifier has to be biased at VREF if the output current
IO is DC coupled.
V+
1998 Nov 03
1
2
IG
)
1
2
IO
I1
140µA
IO
Q4 Q3
A1
+–
Q1 Q2
R1
6.8k
IG
I2
280µA
THD
TRIM
VREF
VIN SR00697
Figure 4. Basic Gain Cell Schematic
5
5 Page 
Philips Semiconductors
Programmable analog compandor
DIP16: plastic dual in-line package; 16 leads (300 mil)
Product specification
SA572
SOT38-4
1998 Nov 03
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet SA572D.PDF ] | |
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