CMOS down conversion mixer

[udaykumarchintala]

I want to know the design procedure for CMOS mixer ,If anyone has any idea please help me.......

 

[mickey_melomane]

CMOS mixers are of two kinds - Active and Passive

1. Active Mixers are of the Gilbert cell type...
2. Passive Mixers are mere switches...

You may refer to any of the RF design books...
For learning about them, Refer to Razavi's "RF Microelectronics", or Thomas Lee's CMOS RF IC Design...

 

[Sadegh.j]

Designing a circuit that only mixes is not all that difficult. You already have an oscillator which oscillates at a desired frequency. You give this to the Emitter of a BJT and Your input signal should go to its base. The output is obtained at the collector, after filtering the desired harmonic out.

Cheers

 

[udaykumarchintala]

yeah.......I have gone through all those books...what my problem is.....while designing any circuit,generally we try to relate the specs and from those we calculate the required bias voltages and widths of the transistors.......how to ralate the same in the mixer as noise figure and 1 dB compression point and others we can not directly formulate.............and how to start the designing process.........

 

[udaykumarchintala]

how to calculate the parasitic capacitance values from the widths and lenghts of a transistor?

 

[udaykumarchintala]

How to measure the extrapolation point for claculating the 1 dB compression point in cadence RF spectre for mixers?????

 

[udaykumarchintala]

How to design the matching circuits for the RF and LO ports while simulating the mixer???please help me.......

 

[lladnar23]

Refer to Tom Lee's book on RFICs for some basic LC matching material.

 

[obovolo]

i think u better take some course at school
or ask ur teacher, TA and ur simulation tool

 

[chintalaudaykumar]

Hii,
In a gilbert mixer The LO transistor should be biased in triode or saturation and why?

Thanks

 

[chintalaudaykumar]

Hii,
In my mixer circuit in the LO ,I have used a pulse source and its peak amplitude is 250mV and source resistance is 100 ohm...so how to claculate the LO power in dBm?and what is maximum LO amplitude that can be used in mixers?

Thanks.......
Uday

 

[imar]

hi!
the LO stage is used as a commutation stage from bloced to saturated not from bloced to linear region.
So the best region is near the threashold region whith out being in linear region.

Added after 5 minutes:

hi!
the LO power is calculated as follows:
Plo= V²lo/R
to convert it in dbm:
Plodbm=10log(Plo/10^(-3)).

 

[fanshuo]

Hii,
In my mixer circuit in the LO ,I have used a pulse source and its peak amplitude is 250mV and source resistance is 100 ohm...so how to claculate the LO power in dBm?and what is maximum LO amplitude that can be used in mixers?

Thanks.......
Uday

the dBm
10*log(0.25)^2/100

Added after 1 minutes:

Hii,
In a gilbert mixer The LO transistor should be biased in triode or saturation and why?

Thanks

in saturation,
in this case the switch contributes no(approximately) noise to the output

Added after 1 minutes:

How to measure the extrapolation point for claculating the 1 dB compression point in cadence RF spectre for mixers?????

check Willy Sansen's paper
"Distortion in elementary transistor circuits"

 

[chintalaudaykumar]

Hii,
The mixer I designed has 1dB compression point .36dBm.RF frequency is 2.4GHz.
For calculating IIP3 I have used second tone as 2.401G in addition to 2.4GHz RF signal.Is it right?
While plotting IIP3 in cadence what should I take as the extrapolation point,because when I change that point the value of IIP3 will change.....Help me.....

Uday