[volt-nuts] Voltage to frequency
DaveH
info at blackmountainforge.com
Mon Jul 29 22:13:13 EDT 2013
The human ear is incredibly sensitive to frequency especially when two or
more notes are played simultaneously.
There is a large group of people who build analog music synthesizers and the
oscillator designs are fairly complex and very very accurate.
Music synthesizers use a scaling of one volt = one octave of pitch change so
there is accurate exponential conversion in the circuit too
These are meant to be played in hot nightclubs as well as air-conditioned
studios to temperature stability is good.
Here is one commercial example ($450)
http://www.synthtech.com/motm300.html
There are a lot of circuits in the public domain -- the old patents have
expired.
Here is Dr. Moog's last oscillator - the 921:
http://experimentalistsanonymous.com/diy/Schematics/Oscillators%20LFOs%20and
%20Signal%20Generators/Moog%20921.jpg
Some of the chips are no longer available so do not plan on copying this
circuit. There are two differential pairs with additional transistors -- one
is used for exponential conversion, the other for sine shaping.
Dave
> -----Original Message-----
> From: volt-nuts-bounces at febo.com
> [mailto:volt-nuts-bounces at febo.com] On Behalf Of Charles P. Steinmetz
> Sent: Monday, July 29, 2013 14:09
> To: Discussion of precise voltage measurement
> Subject: Re: [volt-nuts] Voltage to frequency
>
> Joe wrote:
>
> > Since it is relatively easy and inexpensive to have a very accurate
> > frequency standard at home, I wondered how difficult would it be
> > to use that standard to create an accurate voltage standard.
> >
> > * * * Since this method apparently isn't being used,
> > there must be some reason. Can anyone enlighten me?
>
> As others have said, it is the [in]accuracy of V/F converters and the
> complexity of having to make two accurate modules instead of just
> one. In somewhat more detail:
>
> The V/F conversion can be done open-loop or closed-loop. Let's say
> that from the perspective of a time nut, interesting voltage
> measurements/standards begin at 1ppm. An open-loop solution can't
> come close to that, particularly over temperature and time. On the
> other hand, a closed-loop solution requires building what you are
> after in the first place -- a very accurate voltage reference and
> comparator -- so why bother with the VFC?
>
> When someone designs an open-loop VFC that is linear and accurate to
> better than 1ppm over voltage, temperature, and time, we might have a
> different conversation.
>
> Best regards,
>
> Charles
>
>
>
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