If you have access to the National Semiconductor Linear Applications Data
Books, you will find several function generator circuits which use a diode
network to create the sine curve.  Of course, there is some distortion.
However, a fairly good sine curve can be developed at frequencies below 10
MHz. The diode technique is quite common.

----- Original Message -----
From: "Scott Dattalo" <scott@DATTALO.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, May 17, 2001 5:25 PM
Subject: Re: [EE]: Square Wave Pulse Converted to Sine Wave Pulse


> On Thu, 17 May 2001, Freddie Leaf wrote:
>
> > Hi PICList,
> >
> > I need to generate a sine wave signal for input to an existing
electronic
> > circuit.  The signal will vary in frequency as a function of some other
inputs
> > to a 16F877.  I'm thinking I could generate a 0V to 5V output pulse with
the
> > PIC but need a circuit to convert this signal to a +/- sine wave. The
> > peak-to-peak voltage has to be a least 2.0V.
> >
> > I've experimented with a cap in series with the PIC output, and a
resistor to
> > ground.  This generates a nice positive and negative spike with clean
zero
> > crossings but this is not good enough.  The device I am sending the
signal to
> > is also looking at the slew rate of the signal.  I need a relatively
genuine
> > sine wave.
> >
> > Thanks in advance if you have an ideas.
>
> Instead of filtering a single pulse, you'd be better off filtering a pulse
> stream. All you need to do is generate a series of pulses whose widths are
> proportional to the sine wave amplitude. Low-pass filter this stream, and
you're
> done. Since you're using the 'F877, you can use the on chip PWM peripheral
to
> generate the pulse for you. To obtain the sinusoidal proportional widths,
you
> can try this:
>
> http://www.dattalo.com/technical/software/pic/picsine.html
>
> Scott
>
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>

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