What is a multiplying DAC and what is it used for?

[Learner]

Hello friends,
I was wondering if anyone can explain what is a multiplying DAC and what is it used for?

Can a normal DAC be used as a multiplying DAC by simply adding a Rf to Iout ?

Thanks in advance!

 

[gevy]

Re: Multiplying DAC

Standard DAC have constant voltage reference or narrow range of voltage reference. Multiplying DAC have wide range of voltage reference.
So multiplying DAC may multiply input voltage reference and digital code,
that is output voltage of DAC equals product of input voltage reference and digital code Uout = Uin * N.

 

[Learner]

Re: Multiplying DAC

Why does multiplying DAC have Rf terminal and normal DAC doesnt?

Currently I am looking at the DAC0800 and under its genral decription it mentioned that it can be used as a multiplying DAC but the data sheet does not show how, I do not see the difference between a multiplying DAC and a normal DAC except one has Rf terminal and one doesn't.

How do I use the DAC0800 as a multiplying DAC??

**broken link removed**

 

[bauer]

Re: Multiplying DAC

The DAC fundamentally converts finite-precision numbers (usually fixed-point binary numbers) into a physical quantity, usually an electrical voltage. Normally the output voltage is a linear function of the input number. Usually these numbers are updated at uniform sampling intervals and can be thought of as numbers obtained from a sampling process. These numbers are written to the DAC, sometimes along with a clock signal that causes each number to be latched in sequence, at which time the DAC output voltage changes rapidly from the previous value to the value represented by the currently latched number. The effect of this is that the output voltage is held in time at the current value until the next input number is latched resulting in a piecewise constant output. This is equivalently a zero-order hold operation and has an effect on the frequency response of the reconstructed signal.
Piecewise constant signal typical of a practical DAC output.
Enlarge
Piecewise constant signal typical of a practical DAC output.

The fact that practical DACs do not output a sequence of dirac impulses (that, if ideally low-pass filtered, result in the original signal before sampling) but instead output a sequence of piecewise constant values or rectangular pulses, means that there is an inherent effect of the zero-order hold on the effective frequency response of the DAC resulting in a mild roll-off of gain at the higher frequencies (a 3.9224 dB loss at the Nyquist frequency). This zero-order hold effect is a consequence of the hold action of the DAC and is not due to the sample and hold that might precede a conventional analog to digital converter as is often misunderstood




Multiplying DAC allows o/p voltage to be varied i\p with input reference voltage....