- Just what is a "Polyphase harmonic rejection mixer "
Re: Just what is a "Polyphase harmonic rejection mixer "
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On 2018-01-16 09:00, doug wrote:
On 01/16/2018 07:29 AM, prog wrote:
On Sun, Jan 14, 2018 at 10:41 pm, drew231955 wrote:There is something wrong with this url. I think it's the second / What should the character be?
The main break through with the HF+ is the Polyphase harmonic rejection
mixer. As best I can work out, when converting to base-band, it is an
effective filter for the desired signal and rejects even strong signals
close by with virtually no filtering ahead of the mixer.
It uses multiple phases of the local oscillator to use phasing to reject
its harmonics, but at the same time, and because it is to a 200 kHz
base-band, it rejects everything else too.
The big advantage is not needing a large number of band pass filters like
a direct sampling SDR; the IC-7300 has 15!
The best explanation I have found is a slide show;
It is also subject to patent;
https://www.google.ch/patents/US20110298521?hl=de. One of the authors
wrote the slide show.
Presumably the mixer is a CMOS device, but I have not found one. And the
RF cover on the HF+ is too hard to remove!
Any thoughts on this very novel approach?
Regards Drew VK4ZXI
You can see it as a "super Tayloe mixer". The problem with the original Tayloe Mixer is the harmonic responses at multiples of the LO frequency. The fix is to mathematically suppress these responses by adding more phases. The LO will no longer look like a square wave, but rather like a quantized sine wave. Basically, the more phases you add, the more harmonics you cancel.
This method is combined with narrow band filtering at the mixer itself. There is a switched-capacitor N-Path filter built into the mixer that is tuned using the same LO phases, which provides additional selectivity.
When you see it, all the ingredients required to implement this architecture can be implemented using CMOS silicon, and have a very good "horizontal" and "vertical" scalability: Horizontal with more phases (hence, less harmonics); Vertical with better fab processes (better linearity and NF).
The icing on the cake: This same technology can also work for TX.
The future looks bright!
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