Mixer / transistor pair

[Donnellys]

Hi,


I would like to realize this circuit:
**broken link removed**

But I don't understand how to calculate resistors to have 1v input.:-(

Could you explain me ?



Thanks,
Jérôme

 

[BradtheRad]

Perhaps you are talking about this sentence in the article? "The mixer should be able to take in an input peak of 1V and have a conversion gain..."

I believe 1V means the incoming signal from a previous stage (amplifier). This is typical line level amplitude.

I see resistors labelled what looks like 'Rbias'. Their values are not stated in the schematics. Another diagram shows a resistor network creating the proper ratios of bias volt levels.

We can surmise that the ohm values should not be too low or too high. Typical values might be between 3300 and 100 k.

To find the proper operating point, you'll probably want to adjust values with a potentiometer.

 

[Donnellys]

I believe 1V means the incoming signal from a previous stage (amplifier). This is typical line level amplitude.

Ok but why use a amplifier whereas using resistors ? I mean a bridge resistor

 

[BradtheRad]

Ok but why use a amplifier whereas using resistors ? I mean a bridge resistor

If I understand correctly what you are referring to...

The resistors permit the right amount of voltage/current to operate in the mosfets. The purpose is to bring the mosfets into the correct mode of action.

The circuit appears to be a differential amplifier. There may be a certain amount of amplification of the incoming signal, in addition to its function as a mixer for frequency conversion.

The resistor divider at the right shows the concept for providing the correct bias levels. All the resistors will need to be adjusted to make the differential amplifier work properly.