did you look into magic sinewaves?
http://www.tinaja.com/magsn01.html
seems pretty interesting to me

Peter

----------
> From: GERRY COX <gcox@DEK.COM>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: DC level  to 1KHz sine wave conversion.
> Date: Thursday, February 12, 1998 12:20 PM
>
> My latest project involves a PIC16C73A , which amongst other things,
drives
> a serial 16bit DAC. This gives me a control voltage  programmable from 0
to
> 10V.
> I also need to generate a sinewave of nominally 1KHz. The p-p amplitude
>  must track the DAC voltage and be always 10 percent of its DC  voltage.
> It has to be a reasonably clean and stable sinewave.
> Input voltage range varies from   0.5 to  10V.
> Sine wave output will vary 0 to 1V p-p for the above input range.
Accuracy
> better than 3%.
> Sine wave Total Harmonic Distortion better than 5%
> Sine wave frequency accuracy 1Khz +/- 100Hz
> Output current 5mA max.
> Power supply -  I have +15V, -15V and +5V available.
>
> For example if I have a DC input of 3V the sinewave generator should
output
> 300mV peak to peak at 1Khz.
> this 300mV should be accurate to 309mV max or 291 mV minimum.
>
> I am considering an MF10 switched capacitor filter with clock 128 times
that
> of the 1KHZ output but am looking for ideas
>
> All ideas welcome. Must be reasonably low component count but parts cost
is
> not paramount for a change!
>
> Regards,
> Gerry Cox