Comments on: Asymmetric chopping for improved IM3 | A dead-end research topic?

By: Poojan Wagh

Poojan Wagh — Fri, 19 Mar 2010 03:10:53 +0000

I finally got around to reading your paper, Kevin. Well done. Any way you can generalize it to something other than constant-amplitude tones?

By: Dr. Kevin Gard, NCSU

Dr. Kevin Gard, NCSU — Tue, 07 Jul 2009 02:27:06 +0000

We just published a conference paper on the novel idea of chopping in frequency rather than time to improve IM3. The idea is that you have a two-tone signal where only one tone at a time is selected; therefore, only one tone is presented to the system at a time. The selection rate is much faster than the beat frequency, so the original signal is still passed through. The switched two-tone signal is passed through a presumably wideband nonlinear device. IM3 is not generated by the switched tone signal because only one tone at a time passes through the nonlinear device. The amplified signal is recovered at the output with a filter to remove all the switching aliases.

2009 IEEE International Microwave Symposium
WEPB-3 Low Distortion Amplification of Multisine Signals using a Time-Frequency Technique
G. J. Mazzaro, K. G. Gard, M. B. Steer, North Carolina State University, Raleigh, United States
A novel time-frequency technique is presented for reducing intermodulation distortion when a multisine signal is applied to a nonlinear radio-frequency amplifier. A fast periodic switch is used to apply only one spectral tone at a time to the nonlinear amplifier. A bandpass filter following the amplifier removes switching spurious signals, leaving only the linearly amplified multisine signal at the output. The technique is used to linearize the response of a broadband amplifier with a four-tone uniform phase input signal centered at 465 MHz. The technique yields a 14 dB improvement in intermodulation distortion in comparison to the response of the original four-tone signal at the same output power.

By: Poojan Wagh

Poojan Wagh — Tue, 10 Mar 2009 21:39:00 +0000

Hi, Lior.

I like the way you think! Indeed, I have to work out the math. The important thing is that the nonlinearity of the circuit operates on real values only (it can be seen as a vector with the components being nonlinear, not the entire vector). However, thing might still work out, in that the chopper/”anti-chopper” could be complex-valued.

By: Lior Kravitz

Lior Kravitz — Sun, 08 Mar 2009 12:49:06 +0000

Just a thoguht (didn’t go through the math long enough)- what if I remove the requirement for “real” mixing, and allow quadrature? I think this approach may have some merit, like in using p={j, 1}, and then p^2={-1, 1}.
This may not be immediately practical, but as part of a quadratrure system this might make sense.

By: Poojan Wagh

Poojan Wagh — Thu, 29 Jan 2009 00:44:15 +0000

I eluded to a configuration that had a {0,1} set. What I intended was to have two sets of mixers/lineups and essentially interleave between them. However, I can’t seem to get around the issue that no matter what p^2 has a dc term which allows the IM3 through.

Hopefully, you’ve found a way around it. I look forward to seeing your idea.

By: Dr. Kevin Gard, NCSU

Dr. Kevin Gard, NCSU — Wed, 28 Jan 2009 02:30:21 +0000

The idea of chopping and its relationship to intermodulation distortion is an interesting topic. We are making some interesting progress on a related topic. We have a paper accepted for presentation at IMS2009 on time multiplexed sinusoidal signals to reduce IM3. Time multiplexing uses +1 and 0 switching, but +1,0 and -1 could possibly be used although we have only studied the theory of +1 0 switching.