Best way of changing the output resistance of signal generator or network analyzer?

[mohmohcha]

I want to test an RF frequency divider with high input impedance (gate of MOS).

My question is how I should generate the input signal. If I use normal signal generator or VNA, its output resistance is 50ohm and I will see a very large return loss.

Is there any instrument to generate RF signal with high (or may be even tunable) output resistance? Or is there any good way to boost up the output resistance of the signal generator or VNA.

Thanks.

 

[BigBoss]

You cannot change internal output impedance of a signal generator, it's fixed by design.
But you can use impedance matching between your divider and generator.However, input impedance of a divider is not passive like LNA ( because it works with large signal driven conditions and input stage becomes active when signal edge has arrived) , that's why you should pay some attention about imput impedance of your divider.You may either simulate or ,meausre under large signal driven condition.

 

[biff44]

Well, differential gate inputs want a resistor (usually either 50 or 110 ohms) right at the two input terminals. Some single ended ICs use a resistive load, others are designed to be a 50 ohm match all by themselves. You also might need to DC block the generator from the gate input(s). Which gate are you trying to test?

 

[mohmohcha]

You cannot change internal output impedance of a signal generator, it's fixed by design.
But you can use impedance matching between your divider and generator.However, input impedance of a divider is not passive like LNA ( because it works with large signal driven conditions and input stage becomes active when signal edge has arrived) , that's why you should pay some attention about imput impedance of your divider.You may either simulate or ,meausre under large signal driven condition.

Thanks for your reply first, I will consider that.

But I saw some tunable impedance converter modules before and I am considering to use them.

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Well, differential gate inputs want a resistor (usually either 50 or 110 ohms) right at the two input terminals. Some single ended ICs use a resistive load, others are designed to be a 50 ohm match all by themselves. You also might need to DC block the generator from the gate input(s). Which gate are you trying to test?

Thanks for your reply first.

I am designing an injection locking divider similar to the one in "Yamamoto, K.; Fujishima, M.; “A 44μW 4.3-GHz injection-locked frequency divider with 2.3-GHz locking range,” IEEE J. Solid-State Circuits, Vol 40, pp. 671 – 677, Mar 2005."

The resistance at the inputs will match my circuit, but I don't think it can improve the efficiency.

 

[chuckey]

i would use resistive terminations, leads as short as poss, soldered directly to centre conductor of cable. If your device is sitting in a PCB with a proper coax input connector, then get a "through" term, like a coax adapter but with a 50 ohm resistor in it. If you work with a cable without a proper termination, the level at the far end of the cable can be +- 100% of what it says on the signal generators attenuator.
Frank