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I'm looking for a frequency to voltage converter IC that can operate with an input frequency of around 500 kHz. The device does not have to be high-precision and the operating voltage can be anything. I would be looking for a target price of less than $3.00 each in quantities of 100. I haven't been able to find anything. Thank you.

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How fast can the input signal change? What is its bandwidth? Actually, if you tell us what is the nature of that signal, that would be perfect. – Telaclavo May 31 '12 at 16:08
It is a 500 khz square wave coming out of a 555 with an almost 50% duty cycle. – Fred Paine May 31 '12 at 16:10
\$f_{min}\$=? \$f_{max}\$=? Any resistor or capacitor in the 555 circuit changes its value? If so, according to what? – Telaclavo May 31 '12 at 16:12
Its a simple 555 operating in the astable mode with the output frequency controlled by a single cap and one resistor. Standard operation. – Fred Paine May 31 '12 at 16:22
But, if the resistors and capacitors are fixed, the "nominal" output frequency will also be fixed. So, if you want to measure the variations in frequency of that signal, you basically want to measure the frequency drift, which can be quite low, or difficult to measure without accurate methods. // Why do you want to measure the frequency drift of that 555 output? – Telaclavo May 31 '12 at 16:26

closed as too localized by Kevin Vermeer May 31 '12 at 15:58

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1 Answer

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Use a CD4046 PLL at 1:1 frequency ratio. The VCO is reasonably linear (1%), so its control voltage will be proportional to the input frequency.

Looks like CD4046 sells for $0.15 - $0.20 in quantity: http://octopart.com/partsearch#search/requestData&q=cd4046

Digikey sells them for $0.354 ea in 100 quantity (DIP, other packages cheaper): http://www.digikey.com/product-detail/en/CD4046BE/296-2052-5-ND/

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Thanks for the reply even though they closed me down. Why they consider this question too narrow is beyond me. I've seen lots of other questions on this site that were a LOT narrower in scope than my question. – Fred Paine May 31 '12 at 16:13
I looked at the sheet for this chip, it says voltage to frequency converter, not frequency to voltage. – Fred Paine May 31 '12 at 16:15
@FredPaine It can do both things. If you use just the VCO it includes, you have a V-to-f converter. If you use the VCO and either of the two phase comparators (I recommend you #II), to form a PLL, it can do many things, including f-to-V conversion. // To do V-to-f, take the output from the output of the VCO. To do f-to-V, take the output from the input of the VCO, once you have set up that VCO to work inside a PLL. – Telaclavo May 31 '12 at 16:22
OK thanks. nice tip! – Fred Paine May 31 '12 at 16:31
Can you send me a schematic? my email is mistermustard1@yahoo.com. – Fred Paine May 31 '12 at 16:37
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