Which part of IV curve is used for mixer design?

[parameswari]

iv curve BJT

Hi
i want to design mixer using BJT. Like active region of IV curve is used for amplifier design. Which part of IV curve is used for mixer design?? Why?? . Help me.

 

[srizbf]

Re: iv curve BJT

it can be in linear region .

srizbf
17thmay2010

 

[darcyrandall2004]

Re: iv curve BJT

If you are using a single BJT for a mixer you will need to use the non linear region of the I V curve. If you use the linear region then the output is simply an amplification of the two input signals. y=k(a+b). If you use the non linear region then you will get mixing of the two input signals

 

[WimRFP]

iv curve BJT

Hello,

The process of mixing (frequency conversion) requires you to have a multiply function (z(t) = x(t)*y(t), where x and y are ac functions). This is the only way to get the sum and difference frequency.

One approach is the switch approach where one signal is chopped by the other. By chopping (on-off switching of a signal) you multiply with a square wave. This square wave also contains the fundamental frequency. Example: single or double balanced diode mixers, Gilbert cell.

The other approach is to use an active component in non-linear mode (but without switching it on and off). A BJT has a strong exponential transfer characteristics. By using Taylor Series approximation you will see that you have a product function.

For analog signal processing an established method used conductance modulation of a differential pair. In balanced form this is the "Gilbert cell" mixer. Dual Gate mosfets are also used.

For frequency conversion in telecom, the switch approach is mostly used (with diodes or a hard driven Gilbert cell mixer) as this provides low noise.

Other methods use logarithmic conversion and than sum the signals (as multiplication becomes addition after log conversion). After this exponential conversion is required.

 

[srizbf]

Re: iv curve BJT

yes.
it should be nonlinear region.(as darcyrandall2004 have said).
some mixing has taken in mypart(!)

srizbf
17thmay2010