Question on Stephen A Maas, Microwave mixer

[evoplus]

Hi,

I have some doubts regardin the Stephen A Maas, Microwave mixer which I hoped that you guys can help me clear of.

It mentioned that in the singly balanced mixer part that as both the applied RF voltage and the conductance wave forms are in phase, therefore all the voltage and current components, including the IF frequency must be in the diode. Thus the IF current combine at the node that are joining the diodes.

Question: How does the both the applied RF voltage and the conductance wave forms are in phase? How does the IF appears in the diode?

However the scenario would be different for the LO noise-voltage components shown in figure 2.2(b), these who enter the mixer at the LO port would have a 180° out of phase at the diode. The resulting IF current would be out of phase and be cancelled at the IF output. Therefore as long as the mixer is perfectly balanced, the AM LO noise and the AM spurious signals on the LO would be completely cancelled.

Question: Could someon explain how does the AM LO noise and the AM spurious signals on the LO would be completely cancelled?

Thanks

 

[VSWR]

The LO signal should have sufficient RF level to drive the diodes into clipping. This means conversion loss will be nearly independent of LO drive level. This happens above a certain level, a 'knee'. This means the RF output level of the mixer is more or less independant of the LO drive level and any AM modulation of the LO signal will be suppressed.

Question: Could someon explain how does the AM LO noise and the AM spurious signals on the LO would be completely cancelled? Question: Could someon explain how does the AM LO noise and the AM spurious signals on the LO would be completely cancelled?

 

[evoplus]

Hi VSWR, could you explain more on below

The LO signal should have sufficient RF level to drive the diodes into clipping.

How do the LO signal have sufficient RF level to drive the diodes in the 1st place?
Btw what is the word "clipping" means?

This means conversion loss will be nearly independent of LO drive level. This happens above a certain level, a 'knee'. This means the RF output level of the mixer is more or less independant of the LO drive level and any AM modulation of the LO signal will be suppressed.


What is this level "knee" means? How do we get to this level?

Sorry but could you explain your quote clearly as
I dun really catch your explaination due to my very limited knowledge

Thank a lot

 

[evoplus]

The LO signal should have sufficient RF level to drive the diodes into clipping.

How do the LO signal have sufficient RF level to drive the diodes in the 1st place?
Btw what is the word "clipping" means?

This means conversion loss will be nearly independent of LO drive level. This happens above a certain level, a 'knee'. This means the RF output level of the mixer is more or less independant of the LO drive level and any AM modulation of the LO signal will be suppressed.


What is this level "knee" means? How do we get to this level?


Hi everyone,
It's been a while since I post this but I stlll dun really grasp the concept. Could someone pls kindly advise? Thanks

 

[gundam]

In the first place are the flows of VRF and VLO at diode 2 in the correct direction? Are they supposed to be in opposite directions?

 

[teteamigo]

VRF inphase with g(t)=dId(t)/dVd

If one increase the other increase.

g(t) proportional to increment of VRF


2.2a)
Qualitatively:

an increment in VRF result in a increment of current in opposite direction (decrement in the same direction).

The currents join in opposite phase at IF (Evoplus you are right, there is a mistake)

There is necessity to distinguish signal currents by I1 and I2 that have opposite directions along time to IF node.


The incremental voltages VRF sum in a mesh and the result is a virtual ground for RF at IF port.