Balanced Modulator/Demodulator
AD630
Data Sheet
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Recovers signal from 100 dB noise
2 MHz channel bandwidth
45 V/µs slew rate
Low crosstalk: −120 dB at 1 kHz, −100 dB at 10 kHz
Pin programmable, closed-loop gains of ±1 and ±2
0.05% closed-loop gain accuracy and match
100 µV channel offset voltage (AD630)
350 kHz full power bandwidth
Chips available
RINA
CM OFF
ADJ
DIFF OFF
ADJ
DIFF OFF
ADJ
BIAS
2.5kΩ
AMP A
COMP
CH A+
CH A–
RINB
A
+VS
2.5kΩ
AMP B
10kΩ
–V
10kΩ
5kΩ
Balanced modulation and demodulation
Synchronous detection
Phase detection
Quadrature detection
Phase sensitive detection
Lock in amplification
Square wave multiplication
+VS
VOUT
B
CH B+
CH B–
APPLICATIONS
RB
RA
RF
CHANNEL
STATUS
B/A
COMP
SEL B
–VS
00784-001
SEL A
Figure 1.
GENERAL DESCRIPTION
The AD630 is a high precision balanced modulator/demodulator
that combines a flexible commutating architecture with the
accuracy and temperature stability afforded by laser wafer trimmed
thin film resistors. A network of on-board applications resistors
provides precision closed-loop gains of ±1 and ±2 with 0.05%
accuracy (AD630B). These resistors may also be used to accurately
configure multiplexer gains of 1, 2, 3, or 4. External feedback
enables high gain or complex switched feedback topologies.
The AD630 can be thought of as a precision op amp with two
independent differential input stages and a precision comparator
that is used to select the active front end. The rapid response
time of this comparator coupled with the high slew rate and fast
settling of the linear amplifiers minimize switching distortion.
The AD630 is used in precision signal processing and instrumentation applications that require wide dynamic range. When
used as a synchronous demodulator in a lock-in amplifier
configuration, the AD630 can recover a small signal from 100 dB
of interfering noise (see the Lock-In Amplifier Applications
section). Although optimized for operation up to 1 kHz, the
circuit is useful at frequencies up to several hundred kilohertz.
Rev. G
CM OFF
ADJ
Other features of the AD630 include pin programmable frequency
compensation; optional input bias current compensation resistors,
common-mode and differential-offset voltage adjustment, and a
channel status output that indicates which of the two differential
inputs is active.
PRODUCT HIGHLIGHTS
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The application flexibility of the AD630 makes it the best
choice for applications that require precisely fixed gain,
switched gain, multiplexing, integrating-switching
functions, and high speed precision amplification.
The 100 dB dynamic range of the AD630 exceeds that of
any hybrid or IC balanced modulator/demodulator and is
comparable to that of costly signal processing instruments.
The op amp format of the AD630 ensures easy implementation
of high gain or complex switched feedback functions. The
application resistors facilitate the implementation of most
common applications with no additional parts.
The AD630 can be used as a 2-channel multiplexer with gains
of 1, 2, 3, or 4. The channel separation of 100 dB at 10 kHz
approaches the limit achievable with an empty IC package.
Laser trimming of the comparator and amplifying channel
offsets eliminate the need for external nulling in most cases.
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