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Differential output to single ended output ?

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Junior Member level 2
May 7, 2002
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Is there anyone who knows how to convert a differential output, from a mixer, to a single ended output, using only bipolar transistor.

I found a circuit which use a push pull (common emitter and collector) followed by a follower. The thing is I didn't quite understand this topology.

Any links are welcome, thanks a lot.

a typical device with a differential input is an operational amplifier.
so understand what it does and you know how to do it ...

look at the circuit description in this document
**broken link removed**

circuit which use a push pull (common emitter and collector)
I think this is just a differential amplifier (described in the document)
followed by a follower
this should be a impedance converter or amplifier stage

If I said something wrong please correct me, I'm still in training :oops:


The simplest converter is a differential common emitter pair.
The transistots are connected together at the emitter and biased through a current source from emitters to ground. The diferrential input is at the bases, and the output is at the collector of one of the transistors.

the push-pull amplifier output is single ended,input is differential mode.(it only amplify this mode)

You are not giving us to much of the information about particular mixer that you are using but I am guessingthat you have to use mixer outputs from some RF IC and then interface it to IF filter typically SAW filter.
If that is the case than normally those Mixers implemented in the IC will be Gilbert type which means that you have to provide DC bias at he same ports where you are extracting IF signals. My approach to do soemthing like that is to use high impedance chokes Lc to provide DC bias to those ports. Shunt capacitors Cs at each of those parts should be provided with the basic idea that their impedance should be low for the higher order harmonics so they can be filtered, this can improve somewhat linearity of themixer. Another inductor Lm acroos the IF ports should be added and its value should be selected to resonate with tose shunt caps and parasitic capacitance present at the IF port. Remember that parasitic shunt capacitance is in parallel with those external Cs you have added. Depending on the IF frequency parasitic capacitance can impose limit in the choice of the Cs. After this is done the only thing left to you is basically to add simple resistor across the IF ports that will finaly set IF output impedance and take the IF out from one side of the Lm using dc block capacitor. This network is known as current combining impedance matching network.

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