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I'm trying to come up with a way to create a higher frequency signal from a lower frequency one.

One thing I thought that I would try is to use an active band-pass filter on a square-wave with the frequency bandwidth being a small width centered around a high frequency. In my case I'm using a 100Hz square wave trying to get about a 1kHz signal from it.

My logic behind this is that square waves are just a bunch of harmonics added together to form it's shape with the frequency of the square wave itself being the main wave with the lowest frequency in the bunch, or that's what I gather from the Fourier Series idea.

However... the output wave always seems to be the same frequency as the input wave regardless, so I'm confused as to why this is happening.

Any ideas folks?

Hmm, you picked quite a complicated circuit. I have three suggestions that spring to mind:

1) You an use a PLL IC, though this only works with digital signals (square wave)

2) You could convert your input frequency to a constant voltage (using a frequency to voltage converter), and then convert that voltage back to a frequency (using a voltage to frequency converter), but with 10x more amplification.

3) You could tell us what and why you're doing this, and there may very well be another easier path around it.

TheComet

Well, there's two different applications:

1. I'd like to make a "video controller circuit", most likely utilizing a VGA signal and I'd like to do so using either 74XX TTL logic or 74HCXX CMOS logic. Most of these signals are required to be in the 35 MHz range (at least) from what I can tell.

2. I'd like to see if I could make a FM RF transmitter.


As far as what you said with statements 1 and 2, I originally wanted to make a VCO to do so, but I couldn't figure out how to make a frequency multiplier, so I tried to think of another method of doing this.

EDIT: Also, most of the VCO chips I've looked at cap off at about 1MHz, the same with the fastest 555LC timer I've seen.

Hey! IDK if you're still looking at this, TheComet, but I found a VCO which might work out... the problem is I can't tell what the maximum frequency is for it, only the minimum frequencies. What I'm looking at is a 4046 PLL/VCO (namely the VCO portion). Here's the datasheet for it.

What I'd like to do for the video controller is utilize this as a clock for a PCM video signal (sort of like what DSPs do with audio, i.e. an iPod) but I'm not sure if this is feasible at high frequencies, though I'm sure it would have to be to a degree. Also I'm thinking about changing this from a VGA project to a composite signal, though I might start off with a black & white signal because I'm not sure how I'd superimpose the color burst signal yet.

Also, with the radio... I read that a lot of cell phones nowadays use a VCO for signal transmission/receiving.