|
|
发表于 2021-12-3 08:14:58
来自手机
|
显示全部楼层
本帖最后由 dz20062008 于 2021-12-3 08:30 编辑
单运放带通滤波器电路图
电子产品世界 2011年06月27日
下面是 [单运放带通滤波器电路图]的电路图
A bandpass filter passes a range of frequencies while rejecting frequencies outside the upper and lower limits of the passband. The range of frequencies to be passed is called the passband and extends from a point below the center frequency to a point above the center frequency where the output voltage falls about 70% of the output voltage at the center frequency. These two points are not equally spaced above and below the center frequency but will look equally spaced if plotted on a log graph. The percentage change from the lower point to the center will be the same as from the center to the upper, but not the absolute amount. This is similar to a musical keyboard where each key is separated from the next by the same percentage change in frequency, but not the absolute amount.
The filter bandwidth (BW) is the difference between the upper and lower passband frequencies. A formula relating the upper, lower, and center frequencies of the passband is:
Center Frequency = Square Root of (Lower Frequency * Upper Frequency)
The quality factor, or Q of the filter is a measure of the distance between the upper and lower frequency points and is defined as (Center Frequency / BW) so that as the passband gets narrower around the same center frequency, the Q factor becomes higher. The quality factor represents the sharpness of the filter, or rate that the amplitude falls as the input frequency moves away from the center frequency during the first octave. As the frequency gets more than one octave away from center frequency the rollof approaches 6 dB per octave regardless of Q value. Approximate rolloff rates for different Q values for a single octave change from center frequency are:
Q = 1 = 6 dB
Q = 5 = 18 dB
Q = 10 = 24 dB
Q = 50 = 40 dB
For a single op-amp bandpass filter with both capacitors the same value, the Q factor must be greater than the square root of half the gain, so that a gain of 98 would require a Q factor of 7 or more.
The example below shows a 1700 Hz bandpass filter with a Q of 8 and a gain of 65 at center frequency (1700 Hz). Resistor values for the filter can be worked out using the three formulas below. Both capacitor values need to be the same for the formulas to work and are chosen to be 0.01uF which is a common value usable at audio frequencies. This same filter is used in the Whistle On / Whistle Off relay toggle circuit.
R1 = Q / (G*C*2*Pi*F) = 8/(65 * .00000001 * 6.28 * 1700) = 1152 or 1.1K
R2 = Q / ((2*Q^2)-G)*C*2*Pi*F) = 8/((128-65) * .00000001 * 6.28 * 1700) = 1189 or 1.2K
R3 = (2*Q) / (C*2*Pi*F) = 16 / (.00000001 * 6.28 * 1700) = 150K
这是摘自网上的，鸟语分析
ps:机器翻译如下
单运放带通滤波器电路图
电子产品世界2011年06月27日
下面是(单运放带通滤波器电路图)的电路图
带通滤波器通过一定范围的频率，同时拒绝通带上限和下限以外的频率。要通过的频率范围称为通带，它从中心频率以下的一点延伸到中心频率以上的一点，在该点上，输出电压下降约70%的输出电压在中心频率处。这两点在中心频率上方和下方的间隔不是相等的，但如果绘制在对数图上，看起来是相等的间隔。从底部到中心的百分比变化将与从中心到顶部的百分比变化相同，但不是绝对的数量。这类似于音乐键盘，每个键与下一个键之间的频率变化百分比相同，但不是绝对数量。
滤波器带宽(BW)是上、下通频带频率之间的差值。通带上、下、中心频率的关系式为:
中心频率=(低频*高频)的平方根
品质因数，或滤波器的Q是上低频点之间距离的量度，定义为(中心频率/ BW)，因此当通带在同一中心频率附近变窄时，Q因数就会变高。质量因数表示滤波器的锐度，或当输入频率在第一个倍频程中远离中心频率时幅值下降的速率。当频率离中心频率超过一个八度时，无论Q值如何，每八度的滚动都接近6分贝。从中心频率单倍频程变化的不同Q值的近似滚减率为:
Q = 1 = 6db
Q = 5 = 18 dB
Q = 10 = 24 dB
Q = 50 = 40分贝
对于两个电容值相同的单个运放带通滤波器，Q因子必须大于增益一半的平方根，因此增益98需要Q因子为7或更多。
下面的例子显示了一个1700 Hz的带通滤波器，Q值为8，中心频率(1700 Hz)的增益为65。滤波器的电阻值可以用下面三个公式计算出来。两个电容值需要相同的公式工作，并被选择为0.01uF，这是一个常见的值可用在音频频率。同样的过滤器也用于哨声开/哨声关继电器开关电路。
R1 = Q / C (G * * 2 *π* F) = 8 /(65 * .00000001 * 6.28 * 1700) = 1152或1.1 k
R2 = Q /((2 *问^ 2)- g) * C * 2 *π* F) = 8 /((128 - 65) * .00000001 * 6.28 * 1700) = 1189或1.2 k
R3 = (2*Q) / (C*2* F) = 16 /(。00000001 * 6.28 * 1700) = 150k
那楼主的少一个电阻啥情况
|
|
楼主
