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Macromodel of a Current Steering DAC with ideal switches

Hi,

I'm trying to design a macromodel of a current DAC. The schematic on the left works fine (with MOS). However I want to design with ideal switches, but I'm something because the results aren't what I'm expecting.

To consider:

I'm using the same same parameter for all switches, i.e.:

Open voltage = 100mV

Close voltage = 1V

Open switch resistance = 100M Ohms

Close switch resistance = 10 Ohms

The paralell resistance with the current source is 100M Ohms.

As you can see in the attached image the outputs (iop and ion) from the MOS version are what I'm expecting. However "iopa" and "iona" from the ideal model aren't.

I'am using a resistance load of 10K Ohms which is what I'm using in the sigma-delta modulator (RC filter) feedback.

If someone have any idea I will be glad to hear it.

Thanks in advance.

Andrew Beckett over 10 years ago

The relays aren't wired up correctly. The output of the relay should between iopa and the current source (or iona and the current source), not between avss/avdd and the current source. Also, the input (control) of the relay are connected up incorrectly.

Regards,

Andrew.
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zaratustra over 10 years ago

Dear Andrew,

Thank you very much for your answer.

PS: Sorry for the late reply, I was having some issues with my Cadence account.

Best regards,

Raphael
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