polar
Joined: 23 Aug 2004
Posts: 2
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 23 Aug 2004 17:57 Function Generator Project |
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Hello,
I built this function generator in a class of mine and I get all of my signals. However, My sine wave is a lot smaller then my square wave. How can I boost the wave signal? h**p://www.angelfire.com/bug/kyla/images/func.jpg
thanks,
polar[/url]
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Big Boy
Joined: 20 Jan 2004
Posts: 253
Helped: 10
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| 23 Aug 2004 23:23 Re: Function Generator Project |
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R10 and R11 control the amplification of the sine wave.
To understand this part of the circuit, it is simply using the lays of the op-amps and of owm-law.
First, with the op-amp configured like that, the output is fed back to the inverting input. So, the negative input will try to follow the positive input. If the voltage increase a tiny little bit at the '-' input, then the op-amp output will rush to a lower voltage. Some of that voltage will be fed back through R11, and re-lower the voltage at '-' input. The same apply for voltage increase at '-' input. This will give an end-result that the '-' input will always be almost equal to the '+' input. So, you can assume that within normal opreations of op-amp, it is as if the inverting input is tied to the same voltage as to non-invertine input (which is to GND).
Knowing that the '-' input is 'fixed' to GND, and knowing that the op-amp input take practically no current, then, any voltage before R10 will generate a current through R10 equal to (Vin-GND)/R10 (or simply I=Vin/R10).
That current have to go somewhere. If it's not in the op-amp input (which take practically no current), it will go through R11. The same ohm law apply.
(GND-Vout)/R11=I, or simply I=-Vout/R11.
We can remove I, and isolate the variables
Vin/R10 = I = -Vout/R11
Vin/R10 = -Vout/R11
(Vin/R10)*R11 = -Vout
R11/R10 = -Vout/Vin
Vout/Vin = -(R11/R10).
So, the amplification of the circuit, provided that R10=10K, R11=1K, is -0.1. Note that the output signal is inverted with respect to the input.
To get stronget signal, let's say 4 times stronger, simply find R11/R10 value close to 0.4
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