rf mixer Lo and RF driver mode ?

[manish12]

in what mode the RF and LO driver should be ?

From number of ieee papers and book it is seen that
LO driver should be in saturation and RF driver is in linear / saturation mode.

i am not conform about RF Driver in what it should be ?

can any body confirm this fact .

 

[khouly]

i don't understand
to make the transistor work as amp or driver it should be in active region the active this mean if u use CMOS the active region is Saturation ,

khouly

 

[ieropsaltic]

I think that the RF driver transistors should act as swtches .So, they should operate in linear or saturation region (i.e ON) for those connected to the positive RF signal for half the cycle and should be off for the other half of the cycle and vice versa for the negative RF signal (for differential arrangement as Gilbert Cell) .
For the LO ports, the circuit should appear as a linear one as a usual amplifier thus LO transistors should operate in saturation.But, I'm not sure .
For more details, check chapter 6 at RF microelectronics by Razavi .

 

[manish12]

thankx
but not confirm about it ?
can any one confirm it ?

 

[gszczesz]

You want to modulate the RF signal, but other then that you don't want to distort it. This means you don't want to affect the IP3, IP2, etc... For this to happen, the RF path needs to see linear amplifiers/attenuators.

The commutator is driven by the LO. It needs to switch the polarity of the RF signal, but other then that not to distort it. This means the switches need to look like ideal, low resistance switches during the ON period, and ideal open high-impedance resistors during the OFF cycle. The ideal way to drvie them then is with a strong square wave. This will keep them hard on and hard off during the on/off cycles. This means the LO signal should be driven with a saturated amplifier that creates a square wave.

Take a gilbert cell for example. The bottom diff pair is a linear amplifier that amplifies the RF signal. The 4 switches transistors is the commutator that should be driven with a square-wave LO signal. If the commutator has periods where it is not "hard-on" (i.e. driven with an LO sinusoid), then there will be periods where the switch resistance is going to affect the RF amplitude. Also, a small amplitude on the gate means the RF amplitude can easily affect the forward bias of the transistor, degrading IP3/IP2.

Gregory

 

[manish12]

get it
LO section = in sat mode
RF section = in lin mode

 

[Foufou]

get it
LO section = in sat mode
RF section = in lin mode



I think that both of them must be in saturation mode

 

[safwatonline]

both in sat

 

[najmuus]

RF transistor should be in triode region.

 

[safwatonline]

u cannot get gain from a MOST in triode ,it must be in sat.

 

[nozone]

it's confusing, sometimes we talk about saturation mode, for the amplifier, it's non-linear for the signal, for the cmos transister, it's the normal working area instead of going into triode region, so need to be clarified.

 

[psmon]

Both in saturation. You drive the LO transistors hard, and the RF transistors with small signal.