that1250 THAT Corporation, that1250 Datasheet - Page 7

• Manufacturer Part Number: that1250
• Description: Low Cost, Balanced Line Receiver Ics
• Manufacturer: THAT Corporation

Document 600068 Rev 02
Figure 10. Precision two-input summing circuit
Input 2
Input 1
+24 dBu In
2
3
In Lo
In Hi
In+
In-
9k
9k
7
4
V
V
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
CC
EE
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
U1
THAT1250
9k
9k
3
2
Sense
Vout
Ref
In-
In+
Figure 11. Circuit for audio ADCs with balanced inputs
Figure 12. Automated gain control of a balanced signal
Sense
5
6
1
1
Ref
5
Output
Vout
Copyright © 2008, THAT Corporation
THAT
1256
U2
2
3
6
In-
In+
Sense
Ref
1
Page 7 of 8
5
Vout
THAT
1256
U1
+24 dBu
conversion (degrading CMRR) when there are even
slight differences in gain between the VCAs. A better
approach is to convert the signal to single-ended,
alter the gain, and then convert back to balanced.
receiver to do the balanced-to-single-ended conver-
sion. The VCA section also has a static gain of -3 dB
due to the ratio of R
+24 dBu at its input, since the THAT 1253 output
stage is capable of delivering 21 dBu without distor-
tion. Reducing R
tion in VCA output noise. This arrangement results
in 3 dB greater dynamic range compared to the case
where a -6 dB line receiver and a VCA with zero dB
static gain are used.
restored to 24 dBu by the THAT 1606.
6
In Figure 12 we use a THAT 1253 -3 dB line
2k10
2k10
R19
1/2 Vref of ADC
R8
C4
6n8
3
to 14 kΩ results in a 3 dB reduc-
Low-cost Balanced Line Receiver ICs
R9
249R
2
to R
After the VCA, the signal is
3
. This circuit can accept
AIN+ to ADC
AIN- to ADC
Zero dBu Out
THAT 1250 Series