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Design >> Mixed-Signal Design >> How important is it to test a DAC for dynamic parameters?
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Message started by Mahavir on Mar 18^th, 2009, 5:05pm

Title: How important is it to test a DAC for dynamic parameters?
Post by Mahavir on Mar 18^th, 2009, 5:05pm

I want to know about dynamic parameters testing of DAC.

:question Few details like Is it really important to test a DAC, that achieves all static parameter specifications satisfactorily, for dynamic parameters? Which parameters are important? whether SNR or SFDR or SINAD? Why aren't the on-chip testing methods so popular with mixed signal design as they are with digital design?

Title: Re: How important is it to test a DAC for dynamic parameters?
Post by loose-electron on Mar 18^th, 2009, 10:46pm

A DAC that works perfectly at low clocking rates can be a piece of junk with high clocking rates.

***of course*** you have to test it in a dynamic fashion!!!

Title: Re: How important is it to test a DAC for dynamic parameters?
Post by ywguo on Mar 23^rd, 2009, 2:32am

Mahavir,

It depends on the application. Of course the dynamic parameters are important for a DAC in a RF transmitter. As to SFDR, SNR, SINAD, you need not measure all these parameters. Talk to the system/architecture engineers. But the INL/DNL make sense for a DAC to transmit video signals.

Yawei

Title: Re: How important is it to test a DAC for dynamic parameters?
Post by rf-design on Mar 24^th, 2009, 10:26am

If the circuit dows not contain specific designed time constants which make a difference between DC and AC test a DC test will have a very high coverage. All dynamic effects are then by parasitics. For instance it is very rare that an diffusion diode have a abnormal capacitance but will be leakage free.

Typical current DACs are static circuits. Some errors will be hidden in AC like floating connection. The reverse case is seldom.

Title: Re: How important is it to test a DAC for dynamic parameters?
Post by Bhupendra on Mar 30^th, 2009, 10:42pm

Hi Mahavir,

I guess it depends on application.
If the D/A is used in a low frequency application (like trimming) where monotonicity is all that we care about probably the dynamic performance are not as important.

But for applications where the input bandwidth is defined and you are clocking at a high rate (for example video , SD=6KHz, HD=30KHz) in that case the dynamic performance is what you need to report.

For instance if the D/A is a current steering type then the linearity would be a function of the output impedance which is a function of frequency. The output impedance would be low at high frequency (due to cascode poles) and hence the SFDR would go down.

Similarly when one clocks at high frequencies effects like glitch, charge injection (through switches) and feedthrough come into play and distort the output limiting the dynamic performance.

In all such cases one has to report the SFDR at frequencies of interest (usually the highest frequency in the band).

In some applications a two tone test is also recommended to check for any fold back component in the band.

I hope this helps.

Regards,
Bhupendra