廬
APPLICATION BULLETIN
BY R. MARK STITT AND ROD BURT (602) 746-7445
Mailing Address: PO Box 11400 鈥?Tucson, AZ 85734 鈥?Street Address: 6730 S. Tucson Blvd. 鈥?Tucson, AZ 85706
Tel: (602) 746-1111 鈥?Twx: 910-952-111 鈥?Telex: 066-6491 鈥?FAX (602) 889-1510 鈥?Immediate Product Info: (800) 548-6132
FREQUENCY-TO-VOLTAGE CONVERSION
Precision frequency-to-voltage converters (FVC)s can be
made using voltage-to-frequency converters (VFCs).
Burr-Brown offers a complete line of precision free-run-
ning VFCs.
VFC110
High frequency, low jitter VFC
4MHz max full-scale,
鹵0.02%
typ linearity at
2MHz
VFC121
Precision single-supply VFC (+4.5V to +36V)
1.5MHz max full-scale, 0.03% max nonlinearity
at 100kHz
VFC320
Precision VFC
1MHz max full-scale, 0.005% max
nonlinearity at 10kHz
This bulletin describes three techniques for making a preci-
sion FVC using a VFC. The standard technique has high
precision, but high ripple or slow settling. Adding an output
filter can improve the settling-time, ripple trade-off, but
adds error. A third new technique can eliminate ripple from
the FVC output and improve settling time by more than
1000/1 as compared to the conventional FVC. Moreover,
the DC precision is unaffected.
FVC APPLICATIONS
A rapidly-growing application for frequency-to-voltage
converters is high-voltage analog signal isolation. High-
voltage analog isolation amplifiers (ISO Amps), such as the
Burr-Brown ISO121, are available for isolating signals up
to 8000V. Higher voltage isolation of tens-of-thousands or
even millions of volts as in utility-power-transmission line
monitoring, nuclear event monitoring, and protection from
lightning strikes calls for other techniques. You can get
virtually unlimited isolation by using a voltage-to-frequency
converter (VFC) to digitize an analog signal and transmit it
over a fiber-optic data link to a FVC where the signal is
reconstructed.
Many times VFCs are favored for analog-to-digital conver-
sion because of their integrating input characteristic and
high resolution (modern Sigma-delta analog-to-digital con-
verters are really a variation of a VFC with digital filtering
and encoding). An analog signal digitized by a VFC can be
transmitted to a remote receiver serially over a single
twisted pair wire cable or isolated with a single optical
isolator. At the other end, the digital signal can be both
R
6
40k鈩?/div>
C
3
1
VFC320
V
O
+5V
F
IN
(TTL)
14
13
5
B
14
9
V
S
R
INT
Q
SN74121
One Shot
1
R
0
1k鈩?/div>
1mA
R
1
1k鈩?/div>
10
C
1
1000pF
11 R/C
EXT
1碌s
C
10
EXT
Gnd
A
1
7
3
Q
A
2
4
6
R
2
7.5k鈩?/div>
11
One
Shot
4
12
5
C
2
3300pF
NPO
鈥?5V
+15V
FIGURE 1. A Conventional Frequency-to-Voltage Converter. This FVC can be made by connecting a Burr-Brown VFC320
voltage-to-frequency converter in the FVC Mode. Select C
3
for ripple/settling-time trade off.
漏
1992 Burr-Brown Corporation
AB-040A
1
Printed in U.S.A. June, 1993
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