Differential RF square-wave

[STOIKOV]

rf squarewave

I need to excite a mixer circuit with a 900MHz square-wave differential signal, I mean two signals out of phase 180 degrees.
Is there a signal generator able to provide differential output through two channels ?
If not, how can generate both signals from a signal generatos, maybe an inverter ?

 

[rfmw]

Why exactly do you need square-wave signal anyway?

What you could use is a high-speed logic gate with differential outputs, like ECL driver/receiver MC100EL16 (approx 200ps rise/fall time) or MC100EP16 (approx 100-150ps rise/fall time).

So you connect your 900MHz (single-ended) output from your lab's signal generator to the ECL driver and you get at the output differential square-wave signal, if those rise/fall times meets your square-wave requirements. If not there are logic components with sub 50ps rise fall time and that signal surely looks like a square-wave at 900MHz...

 

[STOIKOV]

I want this differential signal to apply in the input port of a double balanced mixer (local oscillator port)

 

[throwaway18]

About 11cm of coax or pcb transmission line will give you a 180deg phase shift at 900MHz. The exact length depends on the velocity factor of your coax or the geometary of your pcb tracks and the dielectric constant of your board.

Of course you also have to consider impedance matching and reflected power at 900MHz and at the harmonic frequencys present in your square wave.

 

[STOIKOV]

Thanks for your suggestions.
I have no experience with transmission lines, what I can implement is to use a comercial chip as rfmw said or would be better an integrated topology so I could add this circuit to the same chip of my mixer.
I tried with a MOS inverter but the output is not exactly 180 degrees out of phase with respect to the input, that's why I'm still searching for a circuit.

 

[throwaway18]

If you want to get exactly 180degress you are going to have to consider transmission line effects.
A millimeter difference in the length of track that your signal passes through on the way to one of the mixer ports will create a phase difference of a degree or two.

 

[teteamigo]

Use a transformer (v1/v2=1:2) with a center tape , the secondary voltage in two windings are in opposite phase with the reference in center tape.


A circuit with a pair differential convert a signal to two signals in opposite phase.