怎么用运放实现模拟乘法器

tanqiang567

我要用运放做一个分段拟合的正弦波发生器。要求输出正弦波频率f和输出电压U满足：f/U=常数。我的想法是先用分段直线拟合一个输出频率可调幅值固定的正弦波。然后把正弦波乘以当前直线的斜率K这样就能满足f/U=常数。但是我不知道怎么用运放做模拟乘法器。求各位大牛指点啊。或者有什么别的办法能实现电路的要求。求高手指点。

Chilton

An analog muliplexer can be achieved by taking logrithem of each signal, add their outputs together, and take the anti-logrithem of the output of the analog summation circuit.

In your case of U=f/constant, you need to know what that constant is, for example if contant=20dB/dec, then you can simply do a LPF with a single pole at the origin. If contant=40dB/dec, that would be a 2nd order LPF. Circuits to achieve constant in between for example 10db/dec would need more complicated circuits such as RC chain...