THAT1240 Datasheet, PDF (5/8 Pages) List of Unclassifed Manufacturers – Balanced Line Receiver ICs

Rev. 04/29/02
Preliminary Information
Page 5
In Hi
+24 dBu In
In Lo
2
In-
5
Sense
6
Vout
3 ^Ref
In+ U1
R8
2k10
1 THAT
1246
+24 dBu
C4
6n8
AIN- to ADC
R9 _{Zero dBu Out}
249R
2
In-
5
Sense
6
Vout
3 Ref
In+
1
U2
THAT
1246
R19
2k10
U3A _{3 1/2 Vref of ADC}
1
2
AIN+ to ADC
4570
Figure 6. Circuit for audio ADCs with balanced inputs
Since R3=R4 in the THAT 1240, this equation
can be simplified to
a
=
( In +) + Ref
2
The output voltage would then be
Vout = a ´(1 + ^RR₁₂)
Since R2=R1, combining equations results in
Vout = (In+) + Ref
Figure 6 shows a convenient method of driving a
typical audio ADC with balanced inputs. This circuit
accepts +24 dBu in, and using a pair of
THAT 1246s, the signal level between their respective
outputs is +24 dBu. An attenuator network brings
the signal down another 24 dB while attenuating the
noise of the line receivers as well.
The output noise of a THAT 1246 is -109 dBu,
and since there are two of them, the total noise level
going into the resistive pad will be -106 dBu. The
pad reduces the noise level to -130 dBu at the input
to the ADC. The noise density resulting from the line
receivers will therefore be
-3dB
In Lo ₂
In-
5
Sense
6
Vout
In Hi ₃
Ref
In+ _{1 U1}
1243
-3dB
C3
U3
2180B
2 VCC
C2
R2
1
EC+ ⁴
SYM
7
V+
8
IN
OUT
22u ^20k0
V-
GND
EC- ₆
5
3
R4
5k1
Control Voltage
VEE
22p
R3
14k0
2
1
3
U4A
4570
+6dB
C1
VCC
100n
6
4 _{InVccCap27Out+8}
3 _Gnd
Out- ₁
Cap1
Vee ₂
5
VEE
U2
THAT1430
R1
1M0
Out Hi
Out Lo
Figure 7. Automated gain control of a balanced signal
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com