Low-Noise, Differential
Audio Preamplifier IC
THAT1570
FEATURES
Low Noise:
1 nV/√Hz input noise (60 dB gain)
Low THD+N:
0.0003%
≤
30 dB gain
0.0008% @ 40 dB gain
Low Current: 7.5 mA typ
Wide Bandwidth: 4.2MHz @40dB gain
High Slew Rate: 53 V/μs
Wide Signal Swing: >28.7dBu
(±18V supplies)
Gain adjustable from 0 to >60 dB
Differential output
Small 4 x 4mm QFN16 package
Mates with THAT5171
Digital Preamplifier Controller IC
APPLICATIONS
Microphone Preamplifiers
Digitally-Controlled Microphone
Preamplifiers
Differential Low-Noise Preamplifiers
Differential Summing Amplifiers
Differential Variable-Gain Amplifiers
Moving-Coil Transducer Amplifiers
Line Input Stages
Audio
Sonar
Instrumentation
Description
The THAT1570 is a versatile, high performance
current-feedback amplifier suitable for differential
microphone preamp and bus summing applications.
The IC comes in a small QFN package, which saves
PCB space over discrete and other integrated
solutions.
Gain is adjusted via three external resistors (R
A
,
R
B
, and R
G
), making it possible to optimize noise over
a wide range of gains. The 1570 supports the tradi-
tional approach to gain control (viz., THAT's 1510 or
1512) by fixing R
A
and R
B
, and varying R
G
to control
gain. However, the 1570 also supports varying all
three resistors simultaneously with a dual-gang poten-
tiometer or a switched resistor network. This flexible
approach enables the designer to optimize noise over a
wider range of gains than is possible with fixed R
A
and
R
B
.
The 1570's differential output simplifies connec-
tion to differential input devices such as A/D convert-
ers. The part operates from as little as
±
5V up
through
±
18V supplies. Running on
±
18V supplies,
at unity gain, the part accepts >+28dBu input signals.
The 1570 is designed to mate perfectly with
THAT’s 5171 Digital Preamplifier Controller IC. The
part-pair comprises an optimized, digitally controlled
audio preamplifier.
Designed from the ground up in THAT's comple-
mentary bipolar dielectric-isolation process and
including laser-trimmed Si-Chrome thin-film resistors,
the 1570 improves on existing integrated microphone
preamps by offering more versatile gain configuration,
lower noise at low gains, higher slew rate, and lower
distortion.
Pin Name
N/C*
OUT2
OUT1
N/C*
N/C*
Rg1
IN1
N/C*
N/C*
IN2
N/C*
V-
V+
N/C*
Rg2
N/C*
V-
Figure 1. THAT1570 Block Diagram
QFN Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Thermal Pad
Table 1. Pin Assignments
* N/C pins should be left open and not connect to
other traces on the PCB.
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
Copyright © 2015, THAT Corporation. Document 600132 Rev 03
Document 600132 Rev 03
Page 2 of 12
THAT1570 Low-Noise
Differential Audio Preamplifier IC
SPECIFICATIONS
1
Absolute Maximum Ratings
2,3
Supply Voltage (V+) - (V-)
Maximum Input Voltage (V
IMax
)
Storage Temperature Range (T
STG
)
40 V
V+ to V-
-40 to +125 ºC
Operating Temperature Range (T
OP
)
Output Short-Circuit Duration (t
SH
)
Junction Temperature (T
JMAX
)
-40 to +85 ºC
Continuous
+125 ºC
Electrical Characteristics
2,4,5
Parameter
Power Supply
Supply Voltage
Supply Current
Input Characteristics
Input Bias Current
Input Offset Current
Differential Input Offset Voltage
I
B
No signal; either input connected to GND
I
B-OFF
V
OS
No signal;
No signal, Inputs connected to GND
0 dB gain
+60 dB gain
Common Mode
Differential
≥
20 dB gain
40 dB gain
60 dB gain
Common Mode
All gains
R
G
=
∞
—
-2.2
-5.25
-255
(V-) + 4
—
—
—
—
—
6.4
—
—
—
—
58||1
58||3.5
57||28.7
29.4||1.4
26.8
22
+2.2
+5.25
+255
(V+) - 4
—
—
—
—
—
μA
μA
mV
μV
V
MΩ||pF
MΩ||pF
MΩ||pF
MΩ||pF
dBu
V+; -(V-)
I+; -(I-)
Referenced to GND
No Signal
5
—
—
7.5
18
10
V
mA
Symbol
Conditions
Min
Typ
Max
Units
Input Common Mode Voltage Range V
IN_CM
Input Impedance
Z
IN_DIFF
Z
IN_CM
Maximum Differential Input Level
Output Characteristics
Total Differential Output Offset
Common Mode Output Voltage
Maximum Single Output Voltage
Differential Short Circuit Current
Maximum Capacitive Load
V
IN-BAL
G = gain
-(5+0.25*G)
—
(V-) + 2.4
—
—
—
—
26.6
—
-610
—
±
42
±
28
—
400
—
(5+0.25*G)
—
(V+) - 1.4
—
—
100
—
—
mV
mV
V
mA
mA
pF
pF
dBu
V
OSCM
No signal; IN1, IN2 connected to GND
V
OUT-SINGLE
I
SC
C
L MAX
R
L
= 2 kΩ
R
L
= 0
Ω;
Cold start
R
L
= 0
Ω;
Continuous
Over entire temperature range
Stable operation 50% overshoot
R
L
= 2 kΩ
Maximum Differential Output Level
V
OUT
1. All specifications are subject to change without notice.
2. Unless otherwise noted, T
A
= 25ºC, V+ = +15V, V- = -15V.
3. Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only; the functional operation of
the device at these or any other conditions above those indicated in the operational sections of this specification is not impli ed. Exposure to absolute maximum rating condi-
tions for extended periods may affect device reliability.
4. 0 dBu = 0.775 Vrms
5. Unless otherwise noted, R
A
= R
B
= 2.21 kΩ; C
L
= 10 pF
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
Copyright © 2015, THAT Corporation; All rights reserved.
THAT1570 Low-Noise
Differential Audio Preamplifier
Page 3 of 12
Document 600132 Rev 03
Electrical Characteristics (con’t)
1,3,4,5
Parameter
AC Characteristics
Gain Equation
Feedback Impedance
Differential Gain
Power Supply Rejection Ratio
G
DIFF
R
A
, R
B
G
DIFF
PSRR
Programmed by R
A
, R
B
, R
G
(V+) = -(V-);
±5V
to
±20V
0 dB gain
20 dB gain
40 dB gain
60 dB gain
Small signal
≤10
dB gain
20 dB gain
40 dB gain
50 dB gain
60 dB gain
Small signal; R
G
=∞
R
A
= R
B
= 2 kΩ
R
A
= R
B
= 5 kΩ
R
A
= R
B
= 10 kΩ
SR
THD + N
V
OUT
= 10V
P-P
; R
L
=2kΩ ; C
L
=100pF
All gains
V
OUT
= 5V
RMS
; f=1kHz; BW=22kHz
0 dB gain
20 dB gain
40 dB gain
60 dB gain
Inputs connected to GND; f = 1kHz
0 dB gain
6 dB gain
20 dB gain
40 dB gain
60 dB gain
f=1kHz; 60 dB gain
60 dB gain; R
S
= 150
Ω
Differential in to differential out
See Figure 2. (R
G
= R
GV
+ R
GF
)
2
0
—
—
—
—
1 + (R
A
+ R
B
) / R
G
—
—
97
105
105
105
—
70
—
—
—
—
kΩ
dB
dB
dB
dB
dB
Symbol
Conditions
Min
Typ
Max
Units
Bandwidth -3dB
f
-3dB
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
12
10.5
4.2
1.7
600
14
4.2
1.9
53
0.0003
0.0003
0.0008
0.006
18.5
10.4
3.5
1.4
1
1.5
1.5
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
MHz
MHz
MHz
MHz
kHz
MHz
MHz
MHz
V/μs
%
%
%
%
nV/√Hz
nV/√Hz
nV/√Hz
nV/√Hz
nV/√Hz
pA/√Hz
dB
Slew Rate
Total Harmonic Distortion
Equivalent Input Noise Voltage
e
N
Equivalent Input Noise Current
Noise Figure
i
N
NF
Gain Setting
Three external resistors (R
A
, R
B
, and R
G
) set the
gain of the THAT1570. Gain follows the formula:
voltage gain of the part (See Figure 2, in which R
G
is
made up of a fixed (R
GF
) portion and a variable (R
GV
)
portion).
Because all three resistors are external, the
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
R +R
A
V
=1+
A G B
; where A
V
is the (differential)
R
part’s bandwidth will vary with R
A
. The 1570 is
stable with R
A
values of 2kΩ or larger; bandwidth
decreases with increasing R
A
.
The part’s minimum gain is unity (0dB). This
occurs with R
G
open. Maximum gain depends on the
required bandwidth. Full audio bandwidth is
maintained to well beyond 60dB gain.
Other integrated mic preamps which include
internal resistors for R
A
and R
B
(e.g., the THAT 1510
and 1512) allow gain to be varied using one single-
gang potentiometer. The 1570 offers a similar
hookup, by fixing R
A
and R
B
and varying R
G
. This is
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
Copyright © 2015, THAT Corporation; All rights reserved.
Document 600132 Rev 03
Page 4 of 12
THAT1570 Low-Noise
Differential Audio Preamplifier IC
Applications
shown in the circuit of Figure 2.
In such
applications, designers should take care in specify-
ing the pot’s element construction to avoid excess
noise.
The potentiometer taper will set the circuit’s
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
GV
).
Overall gain accuracy depends on the tolerance of
the resistors, including especially the pot (R
GV
) which
dominates R
G
. Theoretically, when R
GV
is zero, the
gain is determined by R
A
, R
B
, R
GF
alone. End resis-
tance (“hop off”) will alter the actual gain; reducing
R
GF
by the amount of end resistance may be appro-
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
A
and
R
B
, since this makes the value of R
G
required propor-
tionately larger for any given gain. The circuit of
Figure 2 shows 5 kΩ resistors for R
A
and R
B
, so for
60 dB gain, R
G
= 10
Ω.
Its noise performance is very
good at 60 dB gain (1.1nV/√Hz, or -133.9 dBu with a
zero ohm input termination, or 1.92 nV/√Hz, or
-129 dBu with a more realistic 150
Ω
input termina-
tion). At minimum gain (6 dB) its noise performance
is still good (21.3 nV/√Hz), or -108.3 dBu with a zero
ohm input termination.
One disadvantage of the circuit of Figure 2 is that
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,
this is ~255 mV. As well, if the wiper of the pot loses
contact with the element, gain will abruptly change to
unity, with an attendant change in dc offset as well.
To minimize dc offsets, consider the circuits of
Figures 5 and 7, which ac couple R
G
.
Improving Noise Performance
The 1570 has extremely low input voltage noise.
To achieve this feature, the input transistors are
large-geometry NPN types, biased at high (~1 mA)
collector current. In order to maintain the low
voltage-noise performance of the 1570, designers
should take care not to present too high a source
impedance to the input pins. A high impedance
generates its own self-noise when not shunted by the
impedance of the source connected to the input pins.
Additionally, the input transistors’ base current,
and any noise in that base current, must be drawn
through the bias network (R
1
and R
2
in Figure 2)
connected to IN1 and IN2 (which connect to the
bases of the input transistors). Any input current
noise will be drawn across the source impedance (as
seen by the inputs), which turns it into a voltage that
is amplified by the gain of the device. Too high a
R
A
5k
+15V
THAT
1570
IN+
R1
1k0
IN-
R2
1k0
-15V
RFI
PROTECTION
R
GV
R
GF
10k 10
IN1
V+
R
G
1
R
G
2
IN2
V-
C9
100n
OUT+
OUT1
OUT2
OUT-
C10
100n
R
B
5k
Figure 2. 1570 Typical Application Circuit Using Single-Gang Pot for Gain Control
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
Copyright © 2015, THAT Corporation; All rights reserved.
THAT1570 Low-Noise
Differential Audio Preamplifier
Page 5 of 12
Document 600132 Rev 03
source impedance can easily spoil the noise of the
device. The 1kΩ resistors used at R
1
and R
2
in
Figure 2 provide a low source impedance for the
1570 even when the input is open, and provide a
2 kΩ (differential) load for the microphone. Higher
source impedances will increase noise seen (and
heard!) with open inputs.
One disadvantage of the single-pot approach is
that noise at low gains is dominated by the noise of
resistors R
A
and R
B
. For the circuit of Figure 2, the
equivalent input noise at 6 dB gain (the minimum pot
setting) is ~21.3 nV/√Hz, or -108.3 dBu. Much lower
noise (~ 11.8 nV/√Hz) can be achieved if R
A
and R
B
are reduced to ~2.5 kΩ, but to achieve 60 dB gain,
this requires R
G
to be = 5
Ω.
(This analysis also
assumes R
GV
= 5 kΩ.)
An alternative offered by the 1570 (and not by
preamps with internal R
A
and R
B
) is that all three
resistors may be varied at once. See the circuit of
Figure 3, which uses a dual-gang potentiometer as
the variable element.
In Figure 3, high gain occurs by decreasing R
G
while simultaneously increasing R
A
and R
B
. The
advantage of this approach is that R
A
and R
B
will
naturally be lower for low gains, without requiring
such a low value for R
G
to achieve high gains. In this
circuit, 60 dB gain occurs with R
G
= 8.66
Ω,
and EIN
is 1.1 nV/√Hz, or -133.9 dBu with a zero ohm input
termination. With a 150
Ω
input termination, the
EIN, dominated by the 150
Ω
resistor, is 1.92 nV/√Hz
or ~ -129 dBu.
This circuit’s minimum gain is 3dB, where R
GV
is
fully CCW. At this gain, the input-referred noise is
~13 nV/√Hz, or -112.5 dBu with a shorted input, and
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.
Of course, other minimum and maximum gains
can be accommodated by varying the resistors at R
A
,
R
B
, R
GV
, and R
GF
.
For variable-gain applications where gain
accuracy is important, THAT recommends using
discrete, switched resistors for R
A
, R
B
and R
G
. With
switched resistors, it becomes even easier to vary all
three resistors to optimize noise.
As with the circuit of Figure 2, R
G
in Figure 3 is
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, gain, and output offset, will change
abruptly. R
3
and R
4
help this situation by minimizing
the change in dc offset generated by the 1570’s input
bias current (drawn across the combination of R
3
in
parallel with the series combination of R
A
and part of
R
A
2k5
R3
10k
IN+
R
GV1
5k
R1
1k0
IN-
R2
1k0
CW
THAT
1570
IN1
R
G
1
R
G
2
IN2
+15V
C9
100n
V+
OUT1
OUT2
V-
OUT-
OUT+
R
GF
8.66
R
GV2
5k
CW
-15V
RFI
PROTECTION
C10
100n
R4
10k
R
B
2k5
Figure 3. 1570 Typical Application Circuit Using Dual-Gang Pot for Gain Control
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
Copyright © 2015, THAT Corporation; All rights reserved.
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