In the past, the rf and lo ports of the mixer on a board were reversed, but the if could still come out normally. Double balanced mixer. Are rf and lo interchangeable? If not, what are the consequences if it is reversed?

Haoyou's mixer architecture is a double-balanced mixer The architecture inside the server is like this, as shown in the figure below. The IF output is at the RF port.

In some textbooks, double-balanced mixing The architecture of the frequency converter is as shown in the figure below. At this time, the IF output is at the LO port.

Then if the position of the IF output is acceptable Yes, does that mean that RF and LO are interchangeable (assuming the performance of the transformers on both sides is the same).

Let’s first analyze the working process of circuit 2.

When VLO is in the positive half cycle, D2 and D3 are turned on, and D1 and D4 are turned off, as shown in the figure below.

When VLO is in the positive half cycle, D1 and D4 are turned on, and D2 and D3 are turned off, as shown in the figure below.

Therefore, during the entire LO cycle, after The current of RL is:

Down Perform a similar analysis for Circuit 1.

When VLO is in the positive half cycle, D3 and D4 are turned on, and D1 and D2 are turned off, as shown in the figure below.

When VLO is in the negative half cycle, D1, D2 is turned on, and D3 and D4 are turned off, as shown in the figure below.

Therefore, during the entire LO cycle, after The current of RL is:

So it is deduced from mathematics From the results, we found that no matter whether the IF output port is at the local oscillator or RF, the current flowing through the IF load is the same.

Therefore, can it be explained that if the performance of the local oscillator, RF terminal and transformer are the same, then these two ports are interchangeable?

Use ADS to perform a simulation verification on the above analysis, as shown in the figure below.

If RF and LO are interchanged, Then it is:

It seems that the frequency conversion loss, There is not much difference in isolation and port VSWR.

Therefore, from the above mathematical analysis and simulation verification, if the performance of the transformer at the RF end and LO end of the mixer is consistent, there will be little performance difference if the two ports are interchanged.