# Arbitrary toggling between 3 voltage levels from 100MHz to 1 GHz, to generate square?

1. ## Arbitrary toggling between 3 voltage levels from 100MHz to 1 GHz, to generate square?

Can anyone suggest what would be some better ways(purchased with minimal work if possible) to generate square waves at 3 tunable voltage levels toggling arbitrarily from one voltage to the other at high speed from 500 MHz to 1 GHz? (ex: 0.1V, 1.5V, 1.5V, 0.1V, 0.35V, 0.1V 1.5V, 0.35V)

I have a Xilinx Kintex 7 KC705 eval kit and can purchase add on boards- the one way I was thinking of that is more conceptually straightforward is to just use a DAC board and drive the outputs at the desired voltages. https://www.abaco.com/products/fmc17...mezzanine-card are ok for a few hundred MHz, but none of the cards can get a ~10-20% of the cycle rise/fall time at 1GHz. For 1GHz arbitrary square waves with say 0.2ns rise/fall times, need about 3.5GHz minimum to get anything, then about >15GHz of analog bandwidth to make it appear "more square". For 500MHz, about ~ 8-10GHz (maybe 5GHz and a less square appearance) analog output bandwith may be ok.

Effectively that is an AWG....Am I thinking about this the wrong way? I don't need all the fancy features of an AWG, but just able to set 3 voltages (0.1V, 0.35V 1.5V) and toggle between then arbitrarily (ideally driven by data patterns out of the Kintex FPGA).

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2. ## Re: Arbitrary toggling between 3 voltage levels from 100MHz to 1 GHz, to generate squ

You might think about using high speed digital logic, e.g. 10 GHz ECL drivers, programmable attenuators, a DC offset source and a resistive combiner to generate the intended waveforms.

A high speed DAC or dedicated analog circuits are the other option. Besides rise and fall time (usually defined for step 10/90% level) more signal quality criteria (overshoot, magnitude accuracy) might be necessary. "Appear square" sounds reasonable at first sight but is actually a rather vague specification.

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In the usual second order system metric, 0.2 ns rise time relates to 1.75 GHz bandwidth.

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3. ## Re: Arbitrary toggling between 3 voltage levels from 100MHz to 1 GHz, to generate squ

To get something that closely matches a square-ish wave you need more harmonics of the fundamental instead of using the rise time requirement. It makes perfect sense that the 15th harmonic is "required" to get something more "square-wave" like.

Maybe you should review Fourier series...
Here is a nice illustration of adding more harmonics to get a better square wave result using excel http://marcuspag.eu/esercitazioni_calc_fourier_en.html

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