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How to make a I/Q modulator?

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Junior Member level 3
Dec 22, 2001
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iq modulator sige

Dear All
Is it possible use discrete components to make a I/Q modulator?


Yes it certainly is possible. Your problem will be matching components for making the carrier feed through initially low and stay low over temperature and time.

This is depend on what kind of modulation you need.

hi, yuhohang

this may usful document from mini circuit.
I&Q and QPSK Modulators/Demodulators: most often asked questions

You need two mixers, a 90 degree phase network. But I would expect pretty poor carrier/sideband supression since the circuit must be very balanced.

theoretically,you can make all ic by discrete componets.but why not use ICs?
yuhohang said:
Dear All
Is it possible use discrete components to make a I/Q modulator?

You should tell us clearly what kind of modulation you need.
Maybe there are existing ICs to fit in with your requirement.
Any example for pi/4 - DQPSK modem ? "Mini" circuits is preferred!

It's obviously possible to make a IQ Modulator.

There will be 8 transistor for full differential Gilbert cell and " Current Transducer " to control the currents of the each pairs.

But some pitfalls may ocur . You may not provide the symmetricity and if
there become 15-20 degree phase error , at the output this will return back with poor sideband rejection and LO rejection.
Instead of this , using ready-to use IQ modulator is more efficient.
Philips SA 900 is very useful Transmit IQ Modulator.
Datasheet and App. report are attached here.


please send me documents about IQ modulator

Hi, BigBoss
can you me send me " design" documents about IQ modulator ?

how to measure accurately a IQ mixer?

A new question:how to measure a IQ mixer's amplitude and phase error accurately?

Now I should design a 9~10GHz IQ mixer,the IF is DC to 100MHz.
As I know,The HP 8753C or HP 8753D's freq offset mode can be used to measure the phase track of IQ mixer,but this network analyses's can not be used up to 6 GHz.whoever know any other method to measure it accurately?

What frequency range do you need?

There are a lot of good integrated circuits available at this moment which are good enough for most applications.

Take for example Analog Devices, Maxim etc.

I mean with above posting something like:
Why making your own I/Q mod with discrete components when cheap and good IC's exists.

Otherwise build your own with some Mini Circuit components if you call that 'discrete'


yuhohang said:
Dear All
Is it possible use discrete components to make a I/Q modulator?

Hi, I am designing one using SiGe Bicmos technology, if you are interested don't hesitate to ask more information.


I want to test baseband circuit.
Modulator has baseband IQ output and Demodulator receive 10.8 MHz input.
Are there any IC match or how to test it anyway.
The only idea I get is to build IQ modulator to output at 10.8MHz
Do you have any idea?


you may use the easy way of R/C and C/R to get the 45degrees and -45degrees phase and using the diode as a MIX.

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