Linear Technology DC961B Demo Manual

Description
Demonstration circuit 961 features an
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 pin. The DC961 board contains an
OCM
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).
Figure 1. DC961B
Fully Differential Amplifier/Driver
LT 1994, low noise, 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
Distortion,
2V
V
Design files for this circuit board are available at
http://www.linear.com/demo/DC961B
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.
V
V
DEMO MANUAL DC961B
Low Noise, Low Distortion,
Differential Input,
P-P
= 3V, f = 1MHz, R = 800Ω
S IN LOAD
2nd Harmonic
3rd Harmonic
1µF
(R )
499
IN
+
IN
+
V
499
0.1µF
–
V
OUT
– +
V LT1994
OCM
0.1µF
+ –
+
V
OUT
1µF
499 499
–
IN
(R )
IN
Figure 2. Typical Application for an LT1994
LT1994
3nV/ Hz
RT
99dBc
96dBc
+ –
(V – V ) 499
OUT OUT
=
+ –
(V – V )
(R )
IN IN
IN
+
A
IN
ADC
–
A
IN
V
CM
dc961b F02
RECOMMENDED ADCs:
LTC2202/LTC2203 AND
LTC2245/LTC2246
dc961bf
1