how to select mixer for a Superheterodyn receiver
The input signal is wideband from tens of MHz to tens of hundreds of MHZ(almost 1 GHz).
IF is about 300MHz。
The mixer needs high IIP3, and low NF.
The mixer need 50 Ohm input and output match. This is the biggest problem.
How can i select mixer? Is Gilbert OK?
If the transconductor of the gilbert is common source, it has good NF and IIP3(use soucre degeneration) . But match to 50 OHm is difficult during such wide band
If i use common gate transconducto, NF is poor.
If i use resistive mixer, IIP3 is good. However, NF is poor and CG is negative.
Anybody can introduce a good structure?
Thank you very much~~~
For your wideband mixer I would recommend to use one of Mini-Circuits models.
For example, their ZAD-2 mixer covers LO/RF from 1 to 1000 MHz, and IF up to 500 MHz. See "www.minicircuits.com", there are many suitable mixers that can suit your application.
To improve receiver noise figure, it is advisable to use one or more low-noise preamplifier(s), again. the same company offers model ZFL-1000LN, with 20 dB gain and ~3 dB NF.
I have used many Mini-Circuits components in addition to my designs, with excellent results. I think their costs are good, too.
You mentioned that you are looking to design a mixer, so buying from a vendor doesn't make sense.
Gilbert mixer is fine for your application. To improve matching you can use balun transformers:
http://www.odyseus.nildram.co.uk/RFI...Cell_Mixer.pdf
Thankd for your reply. I will think about your advice carefully.
Added after 2 minutes:
Thinks for your reply. But i want to design a mixer chip by using MOS technique.
Do you have other good advice?
Hi, steven_l
What exactly gain, iip3 and NF you want to obtain?
Actually， there is no exact performance. IIP3 should be larger than 10dBm, NF should be less than 10dB. CG should be larger than 10dB.
IIP3 is the most important performance, and i need wideband input. Also i need match input and output to 50 Ohm.
Added after 6 minutes:
hi, i have another question.
In the pdf Page 5, the input match can be satisfied by source degeneration and ransformers.
But how about output? In pdf, the load is 500Ohm. If i use ransformers or match net to 50 Ohm, does mean the load become 500Ohm || 500 Ohm=250 Ohm?