1.8V to 1.2V clock signal for ADC testing purposes

[pcca]

Hello,

I need to test some delta sigma modulators.
I would like to ask how to convert a 1.8V single-ended clock to a 1.2V and 0.6V single-ended clock (on a PCB board). Is it possible?
If it is not possible, may your suggest a low-cost clock evaluation board with output clocks of 1.2V and 0.6V?

Kind regards,

 

[betwixt]

It depends on the clock speed. The simplest solution is two silicon diodes in series and then a resistor to ground. Each diode will drop ~0.6V so you have your 1.8V source at the input, 1.2V after the first diode and 0.6V after the second one. In theory it will work at any speed but parasitic effects will become significant as the frequency increases.

Brian.

 

[pcca]

Thanks Brian,

I will think about this solution. The clock frequencies are: 125MHz@1.2V and 10MHz@0.6V.
I will simulate some diodes to see their impact at frequencies up to 100 MHz.

Kind regards.

 

[KlausST]

Hi,

it´s quite unusual that you need such clock signals. What exact ADC are you using?

Klaus

 

[pcca]

Hi Klaus,

They are custom designed delta-sigma modulators in 130 nm CMOS process (1.2V is the typical power supply). The 0.6V clock signal is for a low-voltage modulator, also custom designed.
Our lab is quite new and we do not have a good clock generator yet.

I appreciate your attention.

 

[betwixt]

At those frequencies I suspect simple diode dropers will not be fast enough unless you can sink a lot of current through them. I would love to be proved wrong though so please experiment and let us know the results.

With a voltage as low as 0.6V if you need an active driver you will probably have difficulty with conventional 'totem pole' configurations and you may have to rely on open drain outputs or, if the clock frequency is fixed, an inductive or capacitive voltage divider solution.

Brian.

 

[pcca]

Hi Brian,

I agree with you. But, I will perform some tests using spice simulation at least.
I'll let you know about the solution and this results.

Regards,
PCCA.