Monolithic Synchronous
Voltage-to-Frequency Converter
AD652
The AD652 is available in five performance grades. The 20-lead
PLCC-packaged JP and KP grades are specified for operation
over the 0°C to +70°C commercial temperature range. The
16-lead CERDIP-packaged AQ and BQ grades are specified for
operation over the −40°C to +85°C industrial temperature
range. The AD652SQ is available for operation over the full
−55°C to +125°C extended temperature range.
FEATURES
Full-scale frequency (up to 2 MHz) set by external system
clock
Extremely low linearity error (0.005% max at 1 MHz FS,
0.02% max at 2 MHz FS)
No critical external components required
Accurate 5 V reference voltage
Low drift (25 ppm/°C max)
Dual- or single-supply operation
Voltage or current input
MIL-STD-883 compliant versions available
PRODUCT HIGHLIGHTS
1. The use of an external clock to set the full-scale frequency
allows the AD652 to achieve linearity and stability far
superior to other monolithic VFCs. By using the same clock
to drive the AD652 and set the counting period (through a
suitable divider), conversion accuracy is maintained
independent of variations in clock frequency.
PRODUCT DESCRIPTION
The AD652 synchronous voltage-to-frequency converter
(SVFC) is a powerful building block for precision analog-todigital conversion, offering typical nonlinearity of 0.002%
(0.005% maximum) at a 100 kHz output frequency. The inherent monotonicity of the transfer function and wide range of
clock frequencies allow the conversion time and resolution to
be optimized for specific applications.
2. The AD652 synchronous VFC requires only one external
component (a noncritical integrator capacitor) for
operation.
3. The AD652 includes a buffered, accurate 5 V reference.
4. The AD652’s clock input is TTL and CMOS compatible and
can also be driven by sources referred to the negative power
supply. The flexible open-collector output stage provides
sufficient current sinking capability for TTL and CMOS
logic, as well as for optical couplers and pulse transformers.
A capacitor-programmable one-shot is provided for selection of optimum output pulse width for power reduction.
The AD652 uses a variation of the charge-balancing technique
to perform the conversion function. The AD652 uses an
external clock to define the full-scale output frequency, rather
than relying on the stability of an external capacitor. The result
is a more stable, more linear transfer function, with significant
application benefits in both single- and multichannel systems.
Gain drift is minimized using a precision low drift reference
and low TC, on-chip, thin-film scaling resistors. Furthermore,
initial gain error is reduced to less than 0.5% by the use of laserwafer-trimming.
5. The AD652 can also be configured for use as a synchronous
F/V converter for isolated analog signal transmission.
6. The AD652 is available in versions compliant with
MILSTD-883. Refer to the Analog Devices Military
Products Databook or current AD652/883B data sheet for
detailed specifications.
The analog and digital sections of the AD652 have been
designed to allow operation from a single-ended power source,
simplifying its use with isolated power supplies.
FUNCTIONAL BLOCK DIAGRAM
CLOCK IN
VIN
RIN
CINT
COMPARATOR
D FLOP
LATCH
CK
AND
INTEGRATOR
H
L
D
Q
G Q
D
Q
ONE
SHOT
COS
5V
00798-001
1mA
–VS
Figure 1.
Rev. C
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