在电子工程世界为您找到如下关于“VFC”的新闻
VFC资料下载
基于VFC的大气气压信号测量和硬件设计...
battery and the battery-pack negative contact. An internal voltage-to-frequency converter (VFC) converts this voltage into charge and discharge counts....
2.17 电力遥测中A/D外部电压基准和I/O的调整421
2.18 8031单片机采用V/F转换器的一种软件技巧421
2.19 减少VFC线性误差的一种方法421
2.20 一种高性价卜65一位数字电压表的设计422
2.21 精密DPM的应用422
2.22 单片集成有效值变换器AD536A的原理及应用422
2.23 长时间峰值保持器422
2.24 精密低漂移压流...
jitter VFC4MHz max full-scale, ±0.02% typ linearity at2MHzVFC121 Precision single-supply VFC (+4.5V to +36V)1.5MHz max full-scale, 0.03% max nonlinearityat 100kHzVFC320 Precision VFC1MHz max full-scale...
电压频率转换器VFC接受模拟典雅或电流信号输入，输出一个频率与输入值成比例的脉冲串或方波序列。因此，电压频率转换器可以用作模数转换系统的构建模块...
VFC相关帖子
/jffMMCWt++tOfdpdeeml9kWjfweurZzw8txVAvaLE9bDCCiAsckhhRQO87rLLLvWA41nPela30UYbda973evqyZ/VFC/6c5qFT/Tk4VM+mR1//PE1/LLSqZevHMiKPMjaqgnGI1TFo/aLEwY32kyy+PrYY4+tcb1nkxiFpGQm00RHMYBBuVePQaV+Nq1RBLG99xZvfvOb60mbcE96wxveUE...
19:49 编辑
用VFC是个好主意，只要频率高一些，做到千分之一的误差很容易。提醒注意：大部分VFC电路中用电阻与电容作为定时元件，它们的温度系数是引起误差的一个重要因素。
[quote][size=2][url=forum.php?mod=redirect&goto=findpost&pid=2097649&ptid=507444][color=#999999...
器在使用）。那时LTC6943的10脚被改接到12脚，0.01uF电容被接到运放的反相输入端，其上的电荷（负电压）将使得运放的反相输入端电压下降（等效于在反相输入端与-2.5V之间接入一个电阻），当反相输入端电位下降到低于同相输入端时，运放的输出再次反转。如此反复就形成振荡。由于运放输入端那个1uF电容的充电速率与输入电压有关，所以振荡频率与输入电压有关，就是所谓的VFC啦！
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模数转换器（ADC）ADC音频ADC宽带编码解码器电容数字转换器数字上变频器和下变频器电能计量IC高速ADC集成的接收器带隔离的模数转换器自整角机数字转换器(SDC)和分解器数字转换器(RDC)温度数字转换器视频解码器电压频率转换器(VFC)
编解码器/模拟前端音频编解码器高速编解码器/模拟前端
数模转换器（DAC）音频DAC数字电位计数字上变频器和下变频器直接数字频率合成器(DDS)和...
1.& & 概述电压频率转换器VFC（Voltage Frequency Converter）是一种实现模数转换功能的器件，将模拟电压量变换为脉冲信号，该输出脉冲信号的频率与输入电压的大小成正比。电压频率转换器也称为电压控制振荡电路（VCO），简称压控振荡电路。随电压—频率转换实际上是一种模拟量和数字量之间的转换技术。当模拟信号（电压或电流）转换为数字信号时，转换器的输出是...
VFC(电压频率转换)方式，如图3所示。现场变送器输出模拟量信号(假设电压信号)，电压频率转换器将变送器送来的电压信号转换成脉冲序列，通过光耦隔离后送出。在主机侧，通过一个频率电压转换电路将脉冲序列还原成模拟信号。此时，相当于光耦隔离的是数字量，可以消除光耦非线性的影响。这是一种有效、简单易行的模拟量传输方式。
图3 VFC方式传送信号
当然，也可以选择线性光耦进行设计，如精密线性光耦...
）积分型：
高精度、低成本、高抗干扰能力，分辨率12~16位，转换时间几十~几百ms，采样频率几~几十SPS，价格低。主要用途：数字仪表。
（6）VFC型：
低成本、高分辨率，分辨率8~16位，转换时间几十~几百ms，采样频率几~几十SPS，价格低。主要用途：数字仪表、简易ADC
注：SPS为每秒采样次数
4. ADC及其相应接口电路选择原则
（1）ADC的选用的依据...
本来想写一个总结性的文章的，但是一直也没有时间来完成。月初的时候公司的产品出了点问题，召回了大量产品，虽然是零部件供应商的问题，但作为设计部门也难辞其咎，总是加班到很晚。
现在就我做的简单做一下文字描述吧。
我的这个设计核心部分是一个VFC变换器，也就是电压/频率转换。我对模拟电路不是很了解，根据书上的电路搭了一个电路，但是没有成功。后来chunyang给我...
电路应该比较容易成功的，我对电阻R的选择条件是其流过的电流要远大于运放的Ib，同时小于运放的输出电流。可是试了好多种组合都没有成功起振。不知道这个电路是否还有其他需要注意的事项吗？ 关于VFC的问题 楼主的电路不对，直接用比较器输出来给C放电的时间不对，比较器的输出要接个单稳态电路，频率信号是由单稳态电路产生的，比较器输出用于触发单稳态电路，同时用单稳态电路来给c放电，电路要使用正负电源供电，以地...
电流变换电路
本帖最后由 paulhyde 于
02:57 编辑
电压一频率变换电路（VFC）能把输入信号电压变换成相应的频率信号，即它的输出信号频率与输入信号电压值成比例，故又称之为电压控制振荡器（VCO）。VFC广泛地应用于调频、调相、模／数变换(A/D)、数字电压表、数据测量仪器及远距离遥测遥控设备中。由通用模拟集成电路组成的VFC电路，尤其是专用模拟集成V /F...
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热门资源推荐积分式数字电压表
随着电子科学技术的发展，电子测量成为广大电子工作者必须掌握的手段， 对测量的精度和功能的要求也越来越高，而电压的测量甚为突出，因为电压的测 量最为普遍。同时随着微电子技术的迅速发展和超大规模集成电路的出现，特别 是单片机的出现，正在引起测量控
图 3-2 直流电压测量电路
= T1& &U RC &&& I
U′O1&UO1，则T ′
t1&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& '
图5.1 AT89S51引脚图
e− jω1t& &= r (t )
− &jω t
n&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& ∑
过公式(5)结果为 N &= 213 。数值公式(8)中 N
M&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& 2
and studied
theoretically by the authors [1]. The measurement
procedure uses a digital signal processing algorithm aimed at extracting one of the two periodic
exponential components of a sinusoidal reference signal. By time-domain averaging of the product of the signal &and
the& &th power of the reference
exponential term, the relative
amplitude and phase of any&
&th harmonic of the given signal, normalized
with respect to the given sinusoidal reference, can be obtained. For the digital implementation of this instrument it is important
to choose a suitable
sampling strategy. Thus, to avoid any bandwidth
limitation due to a finite
sampling frequency, an asynchronous
random sampling strategy previously
proposed by the authors was used [2].
&&&&&&&&&&&&&&&&
&&&&&&&&&&&&&&&&&&&&&&&&&&&(1)
&&&&&&&&&&&
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&(2)
Once &the reference exponential term &&is
known, each
Fourier coefficient &can
be derived as the average
of the product of &with
the& &th power of , according
to the well-known formula
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&(3) In order to deduce the reference exponential term &from
, a signal &&&&with a prefixed delay&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& can be intro-
(4) In the particular case of &&, with integer,
(4) coincides
with Euler’s formula.
Since the frequency
of the reference signal is only approximately
known, the quantities &and&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& &
must be estimated. It can easily be shown [3] that&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& can be deduced from the
autocorrelation of the signal&&&&&&&& . For the digital
implemen- tation of its autocorrelation, the signal&&&&&& is sampled
at a sequence of successive pairs of instants&&&&&&&&& &&
&&&&&&&and the quantity &is estimated with a moving
average filter
where&&&& is an integer which
marks a specific value of &deriving &from &a &given &set &of
&sampling &instants.& Thus, &the periodic
exponential signal can be estimated by the following expression:
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
with integer&&&&&&&&&&&&&&&&& (7)
should be approached. Since the delay &is
obtained through a &programmable counter,&&&&&&&&&&&&& can assume
only a set of discrete values and the condition&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& in general can
only be approached. A suitable&&&&& is obtained
by adjusting its value
through a recursive
procedure until &(5) verifies the condition (7) with an approximation such as to guarantee
&&&&&&&&&.
be digitally
determined with a moving average of the last &successive values of the sampled signal &&&multiplied by the
th power of&&&&&&&&&&&&&&& [1]
&&&&&&&&&&&&&
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&with
&&&&&&&&&&&&&&&&&&&&&&&&&&&&(9)
the &unknown constant&&&&&&&&&&&&& represents the &initial shift between the origin of the sampling
sequence and the reference
signal &; &&&&is &the
&mean &sampling-time &interval,
&while &is &the&
&th component of a set of random independent variables having a common continuous uniform
distribution in the interval&&& , with&&&&&&&& . The sequences of the random
Fig. 2 shows a simplified block diagram of the harmonic vector voltmeter. The selected
random sampling strategy im-
plies that the time interval
between two adjacent
sampling instants &can &be &practically
&null, &while &the &distance &of &the following one is not smaller than ; thus, to satisfy
these conditions each &of &the
&three &identical &acquisition channels includes &two &identical
&acquisition &systems &which &operate,
respectively, on alternate
sampling instants [e.g., odd and even in &(9)]. &With &reference
&to &Fig. 2, &the &periodic
the reference
signal &and
the delayed1 &one &&&&&&are
applied &to the second and the third modules (channel
time interval.
When the amplitudes of the two signals coincide, a sampling pulse is generated. To achieve
a continuous random distribution of the sampling instants,
a random white noise of adequate amplitude is added to the output of the DAC.
&&&&&&&&&&&&&&&&&&&&&&
using the adopted asynchronous random sampling
strategy [2], [4]C[6]. Then, implementing
(5) by software, a suitable
value of , giving a sufficiently small&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& must be found [in our
testing procedures, the condition&&&&&&&&&&& is
imposed as a criterion for the search
of a convenient value for &].
generators is &&&&&&&&&&&&&MHz, the delay &can be increased in &steps of 100 ns. The final value of &can
be obtained by adopting a convenient recursive
procedure, which assures an adequate resolution and simultaneously optimizes the search
and lock time, . Then this value can
be used to estimate, through (6), the periodic
exponential signal corresponding to the &reference signal &, &in &order to &evaluate the &spectral
components of the signal &by
software implementing (8).
Each channel
can accept an input signal
in the range
&Each &module &contains
&the &S/H &HA-5340 &device &(gain- bandwidth product 10 MHz,
slew rate 40 V/ &s for 10
V output step) and the ADC HI 674-A
(12 bits, conversion time 15 s), both manufactured
by Harris. The average sampling-time interval is &&&&&&&s (i.e., the mean sampling frequency is
as low as &&&&&&&&&&kHz).
The instrument calibration was performed only in dc con-
ditions,& by &comparison with &the
&HP3458A multimeter and according the manufacturer’s suggested procedure, which re- quires trimming the offset and gain of the ADC until the total
dc error becomes less than&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& 3 mV. The number of successive sampled &values &of &&&&and&&&&&&&&&&&&&&&&&& &&
used &in &the &moving
average filter to estimate&&&&&&&&&&&&&&&&&& through (5) was
&&&&&&&. Also
&the values of &in (8) and&&&&&&&&&& in (10) were selected
equal& to &2& &. To reduce the effect of the noise introduced by &the &acquisition channels and& the
&variance associated to the &sampling
strategy [2], [4]C[6], the mean value of twenty
successive measurements of&&&&&&&&&&&&&&& was considered.
adjusting the phase difference
between the two channels, once a calibration procedure to set the null phase value has been car-
to this end the digital oscilloscope TK2440 was used. The
amplitudes of &and
&were measured with two HP3458A &multimeters. &If &we &recall &that &the &value &of &the average
sampling frequency &was
only 10 kHz, the results
confirm that the adopted
random asynchronous sampling
strat- egy is such as to overcome any bandwidth
limitation deriving from the finite sampling
rate [2], [3]C[5]. Thus, the instrument
bandwidth &practically &depends &only &on &the &bandwidth
&of the S/H adopted in our implementation (i.e., 10 MHz gain-
bandwidth product and a maximum
slew-rate of 40 V/
&s in large signal
operation). As regards
the magnitude accuracy, we obtained an absolute
accuracy&&&&&&&& &&&&&&&&&
and a ratio accuracy&&&& &&&&
; &the &phase &discrepancy was &less
than 0.02 rad. In order
to test the harmonic vector voltmeter
accuracy &under &periodic, &nonsinusoidal &operation,
&different two-frequency signals, including
a fundamental and different order harmonics, were used.
These two frequency signals were generated using the two-channel synthesizer HP 3326A, while the reference signal was provided
by a third function
generator synchronized with the HP 3326A. The amplitude of both the fundamental and the harmonic
was 2 V. The results
given in Table II show good overall
accuracy (better than 1.5% for the
amplitude and 0.03 rad for the phase).
This confirms the broadband capabilities of the signal sampling
and numerical processing procedures adopted. In fact, both the fundamental
and harmonic frequencies are well above not only the average
sampling frequency adopted (10 kHz) but also the maximum
sampling frequency
which, in a conventional
sampling ap- proach, would
be allowed by a 15& &s conversion time of the HI
674-A ADC device. The performances
discussed above were achieved by designing
our prototype instrument according to conventional analog and digital design techniques,
by simply following the state-of-the-art and, in particular, the component
manufacturer’s recommendations. In this respect, it should be noted
that the nonideal behavior of most of the many building blocks in Fig. 1 (e.g., all the components of& the sampling
time generator, except
for the delay
blocks) is not critical
for the instrument accuracy,
since the only requirement on
these elements is producing a pseudorandom
set of sampling instants with a reasonably uniform
distribution. Actually, a good approximation of the required uniform,
pseudorandom sampling time distribution was
this was verified
by measuring the sequence of sampling instants
by means of an HP 3470B universal time interval counter.
Good uniformity of the sampling time distribution was then confirmed by the KolmogorovCSmirnov test.
&In &fact, &the &maximum& absolute difference between the empirical distribution function and the
assumed uniform one was less than 5& 10&&&& . For the test at
the 1% significance level the critical value for&&&&&&&&&&& &
, which is greater than the observed
value 5& 10&&&& . Consequently, our actual significance level
reference were measured. These harmonics
were compared with the theoretical values corresponding
to an ideal square- wave signal characterized by the same true rms value (
V) which was measured
with the HP3458A multimeter.
(11) In the case of the square wave
spectrum given in Table III, the
global rms relative error&&&&&&& , computed
by consider harmonics, was found to be less than 4%, which includes
not only instrument inaccuracy but also test-signal nonideality. The reasonably good overall accuracy
in the measurement of the amplitude and phase spectra
of a square-wave signal is also
qualitatively confirmed by the comparison in Fig. 4 between
the &ideal &and &measured
&waveforms &plotted &by &considering
harmonics.
The implementation of a digital harmonic
vector voltmeter based on a special purpose random sampling strategy
has been presented. The prototype
instrument, based on a floating point DSP, has been tested on different signals, including a single sinusoid with different
phases with respect
to the reference one, &a
&sinusoid& plus &a &single
&harmonic& of &different&
order and a& square wave. In all cases quite good accuracy
both in &magnitude and& phase was &found, even& when the& signal frequency was much higher than the mean sampling frequency. This feature directly derives from the basic properties of the random sampling
strategy adopted and would be practically useful for implementing instruments operating at&
relatively high frequencies.
Pasini was born in Italy in 1964. He
graduated in electronic engineering
from the University of &Bologna, Bologna,
Italy, &where &he is
now a Researcher in Electrical
Measurement.
Gaetano Iuculano
was born in Italy in 1938. He graduated in electronic engineering from the University of Bologna, Bologna, Italy.
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