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Help me design a self-excited BJT mixer in ADS

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ahmad_abdulghany

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Assalamo Alaykom

I want if anyone help me to design a selfexcited mixer ( BJT Mixer ) in general circuit and using ADS tool .. I just want this as a training to the ADS software ..

Thank you very much ..
 

nxing

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Mixer design

Please give more information (or specs), maybe somebody can come up and give you a hand
 

flatulent

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Re: Mixer design

If you use one transistor it will be a very low performance circuit. If you use two transistors the performance will be much better.

The one transistor circuit will be a standard oscillator type with the additional function of coupling the RF signal to the base. The problem will be RF injection into the reverse direction in the RF path with the likely radiation of the LO back out the antenna. The RF signal will also perturb the oscillator frequency making the output at IF be a frequency modulated signal.

For a two transistor circuit you have one transistor for the oscillator and the other for the mixer.
 

ahmad_abdulghany

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Re: Mixer design

What i want to design is a one or two transistor mixers .. but i hope they be BJT for the time being .. if you can help me via sending schematics and design notes or something else ..

Thank you very much
 

flatulent

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Re: Mixer design

I have done a web search and come up with nothing. You should try a local library and look for amateur radio handbooks. The ones by RSGB and ARRL are very good.

To make the mixer start with the standard 4 resistor bjt amplifier setup. Resistors from emitter to ground, collector to power, two from base to ground and power. Put the RF to the base. Put the local oscillator capacitively coupled to the emitter. Use a LO signal level that swings the voltage across the emitter resistor to a large value but not to ground or below. A little experimenting will help you get the highest IF output signal without other problems.
 

ahmad_abdulghany

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Re: Mixer design

flatulent said:
I have done a web search and come up with nothing. You should try a local library and look for amateur radio handbooks. The ones by RSGB and ARRL are very good.

To make the mixer start with the standard 4 resistor bjt amplifier setup. Resistors from emitter to ground, collector to power, two from base to ground and power. Put the RF to the base. Put the local oscillator capacitively coupled to the emitter. Use a LO signal level that swings the voltage across the emitter resistor to a large value but not to ground or below. A little experimenting will help you get the highest IF output signal without other problems.
thank you .. but can't you send me a schematic with typical values .. i think this may be better to me ..
 

flatulent

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Re: Mixer design

I do not have any circuits at hand. Someone else should step in with a diagram scanned from a book.
 

ahmad_abdulghany

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Re: Mixer design

flatulent said:
I do not have any circuits at hand. Someone else should step in with a diagram scanned from a book.
Ok.. suppose that i got a circuit from a text book .. what are the parameters of Mixer simulation ? and how can i get knowledge through this simulation in the ADS software ?
 

flatulent

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Re: Mixer design

You will have to do a time domain simulation and therefore have to know the nonlinearity parameters of the transistor.

I vaguely remember that this type of mixer has an equivalent gain of 1/2 to 1/4 (IF out amplitude/RF input amplitude) compared to the same frequency gain when used as an ordinary amplifier.
 

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