High frequency square to sinewave convertor

[awaiting]

Hello everyone,
i have a 312MHz square wave oscillator and want to generate a 312MHz sinewave with it.i googled it but did not get much info,if anyone can provide some information on how to proceed or any ic capable of it,that would be of much help to me.

Thank you

 

[schip666!]

Depending on how good a sine and how much power you need to get out, you could just put a low-pass RC filter on the output. Or jigger up a better resonant circuit and use the square to drive it. At that frequency you need to be very careful with your wiring and layout.

 

[Phrak]

Goggle "square wave to sine wave filter".

 

[awaiting]

Depending on how good a sine and how much power you need to get out, you could just put a low-pass RC filter on the output.

the square wave generator is giving an output of 0.6Vpp but nothing has been mentioned about the output power,but even -5dBm(316microw) power is acceptable to me.
If i have to use a LPF,the resistor and capacitor values are very low,C=530pF assuming resistor to be 1 ohm,If i increase the resistor value C will go down to a lower value.Do you think this would work?

Goggle "square wave to sine wave filter"

i had checked that before and all the info was about lower frequencies,none in the Mega hertz range.

 

[skeptic2]

You might try using one or more amplifier stages with a tuned LC tank in the collector. Note: a good way to achieve this is to use a coil between the collector and Vcc with a series capacitor from the junction of the collector and coil to the base of the next stage and another capacitor from the base to either Vcc or ground. The two caps and the inductor should be resonant at 312 MHz and the reactance of the shunt cap should be lower than the input impedance of the next stage.

 

[Studiot]

You might try using one or more amplifier stages with a tuned LC tank in the collector. Note: a good way to achieve this is to use a coil between the collector and Vcc with a series capacitor from the junction of the collector and coil to the base of the next stage and another capacitor from the base to either Vcc or ground. The two caps and the inductor should be resonant at 312 MHz and the reactance of the shunt cap should be lower than the input impedance of the next stage.

I agree that's good way, but would like to add that it is important not to overdrive the first amplifier with your square wave - you may need an attenuator.

 

[Phrak]

How sinusoidal do you want it, and at what amplitude? This is doable using a 12 pF capacitor, and around 500 ohms, depending on other requirements. You needn't be freightened off by really low capacitance values. This is what you need at high frequency. At high enough frequencies the capacitor is what obtains from running a lead though a shield and an inductor can be a straight piece of wire.

What are your output and load impedences?

 

[sophiecentaur]

If you want to use a 12pF capacitor then you may need to be careful about stray capacity between other parts of the circuit. This is why people tend to use low impedances RF work. 50Ohms is standard and if you have plenty of power to spare, you might find it worth while using a simple resistive divider circuit before your low-pass circuit.
I must say, I'd be inclined to go for an LC resonator, though, with a small variable C to fine tune it.
But there are so many ways of skinning this particular cat. RSGB are a good source of practical RF circuit ideas.

 

[berkeman]

Hello everyone,
i have a 312MHz square wave oscillator and want to generate a 312MHz sinewave with it.i googled it but did not get much info,if anyone can provide some information on how to proceed or any ic capable of it,that would be of much help to me.

Thank you

BTW, what is the application?

 

[vk6kro]

That frequency seems highly unlikely. Are you sure you mean MEGAHERTZ?

Most oscilloscopes would be unable to observe a square wave at that frequency.

 

[Quinzio]

I agree this frequency is unusually highj for a square wave generator.
To have a good square wave with base frequency at 300MHz you have harmonics at 3GHz or more.
Are you sure about the frequency ?

 

[awaiting]

BTW, what is the application?

i require the sine wave as a local oscillator input for a mixer ic.i have a 100MHz source and need to convert it to 433MHz.It is a part of my B.E. project.

That frequency seems highly unlikely. Are you sure you mean MEGAHERTZ?

yes,i got qfn packaged crystal oscillator ic from Fox electronics.

a good way to achieve this is to use a coil between the collector and Vcc with a series capacitor from the junction of the collector and coil to the base of the next stage and another capacitor from the base to either Vcc or ground

i have forgotten most of my second year engineering stuff,can you please elaborate about the second capacitor from the base to either Vcc or gnd.In what way will the second capacitor help.Also if i connect the LC circuit directly instead of the BJT amplifier will that have any effect on the quality of the wave

How sinusoidal do you want it, and at what amplitude?

only the minimum input power requirement of the mixer is given,that being -5dBm

This is doable using a 12 pF capacitor, and around 500 ohms,

yes,i think this could be a nice solution.instead of 500 ohms,100 ohms is bringing the resonant value close to 300MHz

 

[sophiecentaur]

I don't know why you think a good sine wave is necessary as input to a mixer. A mixer is a very non-linear circuit and it shouldn't give a monkey's about being fed with a square wave L.O. signal. The first thing the signal may encounter will probably be a couple of diodes!

 

[awaiting]

I don't know why you think a good sine wave is necessary as input to a mixer

this may be attributed to the emphasis on theoretical and rote learning in my country(India)!

The first thing the signal may encounter will probably be a couple of diodes!

do u mean inside the mixer ic?
in that case I'm screwed as i thought it to be the reason for not getting the required output.Now have to go back testing.

anyways thank you for your replies and valuable info!

 

[sophiecentaur]

That's not very loyal to your dedicated teachers

What you are seeing on an oscilloscope, connected across the input to the mixer, will only be the Voltage. It does not tell you anything more. Are you worried that it isn't working or that your square wave is just not high enough level for what the mixer data sheet specifies?
Look at the circuits of typical passive mixers. They are usually very simple and based on a bridge of diodes with some form of transformer to apply the L.O. signal across the diodes, switching the incoming signal and beating it up or down to a required IF frequency.

You will definitely need an effective IF filter to extract a clean 430MHz signal from what comes out of the mixer. That will clean things up nicely for you.