No subject

65,500*R  I/O to output.=20
Standard 1% resistors are way more than accurate enough.

If you need more than three Bits, It probable pays to use PWM.=20
To add a PWM use Two equal value resistor in series,=20
with a  total value of 16,384*R connected to a  =20
PWM signal of any freq and add a filter cap between their center and =
ground=20
to filter the small amount of noise that the PWM will be adding.

Note:
For most circuits you do not need to actually add the output resistor,=20
there is always some places to add a little offset to.
All you need to do then, is find a place that you can change the offset=20
value of the DAC output, and add a small filtered current into it thru a =
resistor / filter divider.
The total zero range you need to add will depend on the number of Dac =
bits you have.

As an example to expand a 5 volt 14 bit Dac, to 16 (or to 24) bits, =
connect=20
the additional Dac thru a RCR filter to a point that will change the=20
Main Dac's output to offset by up to 0.3051 mV (minus the value of one =
of the added bits)

One way to turn a Really good 18 bit Dac into 24 + bits, is scale a 6 =
bit Dac=20
thru a resistor to some place on the 18 bit dac that will add 0 to 18.78 =
uV=20
+ - < 1/2% of offset onto the 18 bit Dac's output.

Have Fun
WarrenS

*****************************

Poul, how do I PWM a DAC that is itself a PWM device? This question =20
is prompted by the DAC I'm using in Bert Zauhar's FLL GPSDO, which is =20
a dithered 10-bit DAC in a PIC chip that results in 14-bit =20
resolution. I'd like to have a simple way to get 2 to 4 extra bits of =20
resolution out of this. Can you recommend some design resources to do =20
this?

Dick Moore