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| 型號： | LB-45 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Frequency-to-Voltage Converter uses Sampleand- Hold to Improve Response and Ripple |
| 中文描述： | 頻率至電壓轉(zhuǎn)換器使用Sampleand持有的提高反應(yīng)和紋波 |
| 文件頁數(shù)： | 1/2頁 |
| 文件大?。?/td> | 82K |
| 代理商： | LB-45 |
TL/H/8494
F
t
L
National Semiconductor
Linear Brief 45
April 1979
Frequency-to-Voltage
Converter uses Sample-
and-Hold to Improve
Response and Ripple
Most frequency-to-voltage (F-to-V) converters suffer from
the classical tradeoff of ripple versus speed of response.
For example, the basic F-to-V converter shown below has
13 mVp-p of ripple, and a rather slow 0.6 second settling
time, when C
FILTER
is 1
m
F. If you want less ripple than that,
the response time will be even slower. If you want quicker
response, it is easy to decrease C
FILTER
, but the ripple will
increase by the same factor.
The improved circuit in Figure 2 makes an end-run around
these compromises. A low-cost sample-and-hold circuit
such as LF398 can sample the F-to-V’s output at the peak
of its ripple, and hold it until the next cycle. The LF398 has
fairly low output ripple (rms) but it does have some short
duration noise spikes and glitches which can be removed
easily with a simple output filter. The ripple at the output of
the active filter V6 is smaller than 1 mV peak, but the set-
tling time for a step change of input frequency is only 60 ms,
or ten times quicker than the ‘‘basic’’ FVC with C
FILTER
e
1
m
F.
V
OUT
e
f
IN
c
#
R
L
R
S
J
c
(1.9V)
c
(1.1R
t
C
t
)
#
output
ripple
p-p
J
e
#
1
C
FILTER
J
c
(1.9V)
c
(1.1R
t
C
t
)
R
S
TL/H/8494–1
FIGURE 1. Basic Frequency-to-Voltage Converter
TL/H/8494–2
FIGURE 2. Improved F-to-V Converter Using Sample-and-Hold
C
1995 National Semiconductor Corporation
RRD-B30M115/Printed in U. S. A.
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