AD650 Analog Devices, Inc., AD650 Datasheet - Page 17

• Manufacturer Part Number: AD650
• Description: Voltage-to-frequency And Frequency-to-voltage Converter
• Manufacturer: Analog Devices, Inc.

PHASE-LOCKED LOOP F/V CONVERSION
Although the F/V conversion technique shown in Figure 13 is
quite accurate and uses only a few extra components, it is very
limited in terms of signal frequency response and carrier feed-
through. If the carrier (or input) frequency changes
instantaneously, then the output cannot change very rapidly due
to the integrator time constant formed by C
is possible to decrease the integrator time constant to provide
faster settling of the F-to-V output voltage, the carrier
feedthrough then becomes larger. For signal frequency response
in excess of 2 kHz, a phase-locked F/V conversion technique
such as the one shown in Figure 22 is recommended.
CONTROL
–5 VOLTS
INPUT
GND
–V
+V
S
S
CARRIER
CARRIER
AUTO ZERO
VFC NORMAL
INPUT
2
3
1
2
3
4
5
6
7
INPUT
1
4
AD7512
AD582
11
3
–V
10
D
FREQ
5
INT
D
S
CLOCK
CLOCK
OUT
12
2
2
1
1
1
PR
and R
1/2 7474
1/2 7474
PR
4
10
+V
14
13
12
11
10
6
9
9
8
2
VOLTAGE
1
S
D TYPE FLIP FLOP
AD650
1MHz FULL-SCALE
R
C
C
(UNIPOLAR INPUT)
INPUT
1
2
CLEAR
Figure 22. Phase-Locked Loop F/V Conversion
IN
OS
INT
0.1µF
8
7
CAP
CLEAR
13
1
IN
= 16.9k
16.9kΩ
OUTPUT
= 51pF
= 1000pF
. While it
Q
2
Q
1
2
1
10kΩ
Figure 21. Autozero Circuit
9
5
3
+V
3
2
Rev. D | Page 17 of 20
1000pF
1/4 7400
S
+IN
–IN
1kΩ
200kΩ
NAND
4
NULL
BIPOLAR
OFFSET
0.5mA
VOLTS INPUT
TO AD650
14
2
1
1000pF
OP
AMP
–15V
13
5
71.5kΩ
4
5
SD211
DMOSFET
In a phase-locked loop circuit, the oscillator is driven to a
frequency and phase equal to an input reference signal. In
applications such as a synthesizer, the oscillator output
frequency is first processed through a programmable “divide by
N” before being applied to the phase detector as feedback. Here
the oscillator frequency is forced to be equal to “N times” the
reference frequency. It is this frequency output that is the
desired output signal and not a voltage. In this case, the AD650
offers compact size and wide dynamic range.
XOR
–V
590kΩ
0.1µF
1mA
7486
1
S
–0.6 VOLT
–V
+15V
+V
9
COMPARATOR
12
S
COMPARATOR
INPUT
6
–15V
3.6kΩ
S
0.1µF
S
ANALOG
GND
GND
B
G
11
D
SHOT
51pF
ONE
51pF
C
FREQUENCY
AD509
OP AMP
6
15pF
VOLTAGE
140kΩ
OUTPUT
AD650
C
OUTPUT
OS
R
DIGITAL
F/V
GND
10
8
FREQUENCY
OUTPUT
500Ω
10µF
+
+5V
AD650