that1570 THAT Corporation, that1570 Datasheet - Page 6

• Manufacturer Part Number: that1570
• Description: Low-noise, Differential Audio Preamplifier Ic
• Manufacturer: THAT Corporation

Document 600132 Rev 01
is essentially no different with a 150 Ω input termina-
tion. This is about 4.2 dB better than the circuit of
Figure 2 at its minimum gain (6dB). Note also that at
the minimum +3 dB gain and ±18 V rails, the circuit
of Figure 3 can accept up to +25.7 dBu input signals
without clipping. This offers more headroom than
the circuit of figure 2.
can be accommodated by varying the resistors at R
R
accuracy is important, THAT recommends using
discrete, switched resistors for R
switched resistors, it becomes even easier to vary all
three resistors to optimize noise.
dc coupled. This means that the differential output
offset voltage will vary with gain. Also, if the wiper of
either half of the gain pot loses contact with the
element,
abruptly. R
the change in dc offset generated by the 1570’s input
bias current (drawn across the combination of R
parallel with the series combination of R
R
performance, consider the circuits of Figures 6 and 8
which ac-couple R
B
GV1
, R
IN+
Of course, other minimum and maximum gains
For
As with the circuit of Figure 2, R
IN-
, or the other mirror half). Again, for best dc
GV
, and R
variable-gain
gain,
3
and R
PROTECTION
GF
Figure 5. 1570 Typical Application Circuit With Single-Gang Pot for Gain Control, AC-Coupled R
.
and
G
4
.
RFI
help this situation by minimizing
output
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
applications
Copyright © 2009, THAT Corporation; All rights reserved.
1k0
R1
offset,
A
, R
G
B
R2
1k0
in Figure 3 is
and R
where
will
A
and part of
R
10k
GV
G
change
. With
gain
3
in
A
Page 6 of 12
,
R
10 3300u
GF
C
Inputs
Simple Configurations
tion diodes at all pins except V
diodes reduce the likelihood that accidental electro-
static discharge (ESD) or electrical over stress (EOS)
will damage the ICs. Other diodes across the base-
emitter junctions of the input transistors prevent
excessive reverse biasing of these junctions (which
would degrade the noise performance of the input
devices).
G
RG2
Figure 4. 1570 Equivalent Circuit with Internal Protection
RG1
Vee
Vcc
IN1
IN2
As shown in Figure 4, the 1570 includes protec-
THAT
1570
IN1
R
R
IN2
G
G
1
2
-15V
+15V
Vcc
Vee
R
5k
R
A
5k
B
100n
C10
100n
OUT1
OUT2
C9
Differential Audio Preamplifier IC
Diodes
THAT1570 Low-Noise
CC
-A
-A
V
V
G
and V
OUT+
OUT-
EE
. These
OUT1
OUT2