1
dc961bf
DEMO MANUAL DC961B
Description
LT1994
Low Noise, Low Distortion,
Fully Differential Amplifier/Driver
Demonstration circuit 961 features an
LT
®
1994
, low noise,
low distortion, fully differential amplifier. The LT1994 is a
high precision, very low noise, low distortion, fully differ-
ential input/output amplifier (see Table 1). The LT1994’s
output common mode voltage is independent of the input
common mode voltage, and is adjustable by applying a
voltage on the V
OCM
pin. The DC961 board contains an
LT1994 amplifier configured as a unity gain differential
amplifier with 499Ω feedback and input resistors. Gains
greater than one require changing the input resistors to
a value lower than 499Ω (refer to Figure 2). In addition,
DC961 has surface mount pads and traces for resistors
and capacitors for building first and second order fully
differential filter circuits. The differential outputs of DC961
can be configured with a first order RC network for driv-
ing the differential inputs of an analog-to-digital converter
(ADC).
L
, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Analog
Devices, Inc. All other trademarks are the property of their respective owners.
Connection to the differential input and output of a DC961
is through SMA connectors. Onboard jumpers configure
the DC961 for dual or single power supply operation. The
differential input of a DC961 is AC coupled with 1µF capac-
itors for ease of use as a dual or a single supply circuit.
DC coupling to the DC961 input is provided through the
shorting of the input capacitors with 0Ω surface–mount
resistor jumpers.
Table 1. LT1994 Noise and Distortion
Differential Input Referred Voltage Noise
Density
3nV/
RT
Hz
Distortion,
2V
P-P
Differential Input,
V
S
= 3V, f
IN
= 1MHz, R
LOAD
= 800Ω
2nd Harmonic
3rd Harmonic
99dBc
96dBc
Design files for this circuit board are available at
http://www.linear.com/demo/DC961B
Figure 1. DC961B
Figure 2. Typical Application for an LT1994
V
OUT
–
V
OUT
+
V
+
0.1µF
dc961b F02
499Ω
(R
IN
)
(R
IN
)
V
IN
+
V
IN
–
499Ω
499Ω
499Ω
RECOMMENDED ADCs:
LTC2202/LTC2203 AND
LTC2245/LTC2246
1µF
1µF
0.1µF
A
IN
–
A
IN
+
ADC
+
–
–
+
LT1994
V
OCM
V
CM
(R
IN
)
=
(V
OUT
+
– V
OUT
–
)
499Ω
(V
IN
+
– V
IN
–
)
