that1570 THAT Corporation, that1570 Datasheet - Page 4

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

Document 600132 Rev 01
Gain Setting
gain of the THAT1570. Gain follows the formula:
voltage gain of the part (See Figure 2, in which R
made up of a fixed (R
portion).
designer is free to select them for best noise perform-
ance at the desired gain setting(s). Note, however,
that as with any current-feedback amplifier, the
part’s bandwidth will vary with R
stable with R
decreases with increasing R
occurs with R
required
maintained to well beyond 60dB gain.
internal resistors for R
and 1512) allow gain to be varied using one single-
gang potentiometer. The 1570 offers a similar
hookup, by fixing R
shown in the circuit of Figure 2.
applications, designers should take care in specifying
the pot’s element construction to avoid excess noise.
IN+
Three external resistors (R
A
Because all three resistors are external, the
The part’s minimum gain is unity (0dB). This
Other integrated mic preamps which include
IN-
V
=1+
bandwidth.
R
A
A
G
R
PROTECTION
+R
G
open. Maximum gain depends on the
values of 2kΩ or larger; bandwidth
B
; where A
A
RFI
and R
GF
Figure 2. 1570 Typical Application Circuit Using Single-Gang Pot for Gain Control
A
) portion and a variable (R
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
Full
and R
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
A
B
.
and varying R
V
audio
B
Copyright © 2009, THAT Corporation; All rights reserved.
A
, R
(e.g., the THAT 1510
is the (differential)
1k0
R1
B
, and R
A
. The 1570 is
bandwidth
R2
1k0
G
G
In such
) set the
. This is
R
10k
Applications
GV
G
GV
is
is
Page 4 of 12
)
R
10
GF
characteristic of gain vs. pot rotation. Typically,
reverse log (audio) taper elements offer the desired
behavior in which gain increases with clockwise
rotation (and lower values for R
the resistors, including especially the pot (R
dominates R
gain is determined by R
tance (“hop off”) will alter the actual gain; reducing
R
priate, especially if the end resistance is consistent. It
will be easier to maintain consistent gain at the high-
gain end of the pot travel at higher values for R
R
tionately larger for any given gain. The circuit of
Figure 2 shows 5 kΩ resistors for R
60 dB gain, R
good at 60 dB gain (1.1nV/√Hz, or -133.9 dBu with a
zero ohm input termination, or 2.27 nV/√Hz, or
-127.7 dBu with a more realistic 150 Ω input termi-
nation). At minimum gain (6 dB) its noise perform-
ance is still good (21.3 nV/√Hz), or -108.3 dBu with a
zero ohm input termination.
differential dc offset at the 1570 output will vary with
gain. At 0 dB gain, the 1570’s worst-case differential
output offset voltage is ~5 mV, while at 60dB gain,
GF
B
, since this makes the value of R
THAT
1570
The potentiometer taper will set the circuit’s
Overall gain accuracy depends on the tolerance of
One disadvantage of the circuit of Figure 2 is that
by the amount of end resistance may be appro-
IN1
R
R
IN2
G
G
1
2
+15V
-15V
G
Vcc
Vee
G
. Theoretically, when R
R
5k
= 10 Ω. Its noise performance is very
R
A
5k
100n
100n
B
C10
C9
OUT1
OUT2
Differential Audio Preamplifier IC
A
, R
B
, R
GV
THAT1570 Low-Noise
GF
).
G
alone. End resis-
required propor-
A
GV
and R
is zero, the
OUT+
OUT-
GV
B
) which
, so for
A
and