Re: [請益] RF MIXER
Hey Lary thanks for your opinion!
Sorry I am not in Taiwan and need to use English typing sys.
Yes, I agree with you zero-IF has some DC issue compared with low-IF.
However, we are not necessary to use "physical" HPF to deal with that in
the industry.
Why I said maybe you are talking about zero-IF system is because of the
image rejection issue.
Because the image of zero/low-IF system is usually located in your own
application band, it is impossible to design a image rejection filter to
kill them. That's why we need image cancellation Mixer/sys.
Sure, as you said the mismatch of IQ path will degrade the image rejection,
if we don't do any correction I think maybe only ~ -40dB we can get in current
technology.
In heterodyne system, it is a different story. If we can choose the IF cleverly
then the image can be located some less interference band and we don't need
high rejection level.
Also, the IF selection will affect the channel filter and image(band) filter
design. In most cases, they are directly trade-off.
Anyway, really appreciate your idea and I agree with you direction conversion
type sys is the main-stream now and maybe IQ mismatch has more effect on the
image issue.
※ 引述《Lary (PTTuser)》之銘言：
: 推 poppyya:嗯~ 謝謝各位^^ 114.46.113.58 09/11 00:27
: → poppyya:再問一下喔~ IF 中頻 要去哪裡查? 114.46.113.58 09/11 00:31
: → poppyya:我的意思是 如果我做2.4GHz的MIXER 那IF? 114.46.113.58 09/11 00:31
: → poppyya:這要到哪裡才查的到??? 謝謝了!! 114.46.113.58 09/11 00:32
: → Lary:也許你應該先說妳到底要做什麼樣的系統? 123.195.2.141 09/11 00:38
: → Lary:不同調變方式需要不同的頻寬 這可能需要做 123.195.2.141 09/11 00:39
: → Lary:system或baseband的人來訂到底if的center 123.195.2.141 09/11 00:40
: → Lary:freq. 和band width是多少 然後決定DAC到 123.195.2.141 09/11 00:41
: → Lary:mixer間的LPF design 123.195.2.141 09/11 00:41
: 推 Gocoba:不同的架構有不同的IF 同時也牽扯到Image 72.222.132.58 09/11 01:12
: → Gocoba:rejection的問題 還有filter的設計 72.222.132.58 09/11 01:12
: → Lary:image rejection感覺跟poly-phase filter 140.113.228.149 09/11 17:29
: → Lary:以及LO的I-Q error比較有關係ㄟ... 140.113.228.149 09/11 17:30
: 推 carrack:Lary, you are talking about zero-IF sys 63.239.159.137 09/11 23:44
: → Lary:I am talking about low IF system 60.250.197.166 09/12 11:53
: → Lary:I'm not sure if the mixer design is differ 60.250.197.166 09/12 12:02
: → Lary:ent for zero-IF and low-IF. However, the 60.250.197.166 09/12 12:02
: → Lary:difficult part of zero-IF design would be 60.250.197.166 09/12 12:03
: → Lary:how to remove DC offset due to device mism 60.250.197.166 09/12 12:04
: → Lary:atch or other factors without affecting th 60.250.197.166 09/12 12:04
: → Lary:e wanted signal. A HPF with very low 3dB 60.250.197.166 09/12 12:05
: → Lary:freq will need a large layout area and lon 60.250.197.166 09/12 12:06
: → Lary:g stable time. I did not do it myself. 60.250.197.166 09/12 12:07
: → Lary:I do not know it very well and we can 60.250.197.166 09/12 12:09
: → Lary:discuss if you are interested. 60.250.197.166 09/12 12:09
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