Limiter distortion level at small signal input

[hosein_rabiee_g]

Hi everybody.
I used a coaxial PIN diode limiter to protect my receiver blocks.
its limit the power at +20dBm. but at above -10dBm input power, the harmonics of input comes up and detected in receiver.
my question is, which parameter of detectors is important for harmonics level below limiting threshold of limiter?
thanks

 

[jiripolivka]

A good limiter is a linear device until signal amplitude increases to be limited or distorted. A PIN diode limiter usually consists of a PIN-diode attenuator which is a linear device, and a detector diode that controls PIN diode loss. Together the deice behaves like a limiter but the limiting threshold can be adjusted by DC bias circuit.

Not knowing details of your circuit it is difficult to decide why harmonics occur at -10 dBm; it may be due to the detector alone. A detector without DC bias starts "opening" the diode at above -20 dBm and it generates harmonics. Try to DC-bias your detector so it opens above +10 dBm or more to prevent it from generating harmonics.

 

[biff44]

I agree, if you use a 2-diode limiter, it will hold its linearity better at moderate powers. This is because you can use a limiter diode with a thicker I region, so there is less rectification/conduction at microwave frequencies.

 

[hosein_rabiee_g]

Thanks. I want to buy another PIN limiter. Which parameters of Limiter determine the harmonics of limiter at moderate power below limiting?
and from which parameter of limiter in its datasheet, I can guess the behavior of limiter in small signal region? If I have to buy a specific class of limiter, what is

 

[jiripolivka]

Thanks. I want to buy another PIN limiter. Which parameters of Limiter determine the harmonics of limiter at moderate power below limiting?
and from which parameter of limiter in its datasheet, I can guess the behavior of limiter in small signal region? If I have to buy a specific class of limiter, what is

I am afraid no manufacturer of limiters specifies its harmonic distortion at low signal levels.

You can buy or make a suitable limiter and take the data you need. Or, use a low-pass filter after it to reduce the harmonic output.

 

[ltrlspree]

which frequency and OP1db is required?

there are some low power limiters out there like ASML series from Avago


the datasheet shows how the second harmonic grows with input power. Perhaps that gives some reference/ideas.

Br

 

[hosein_rabiee_g]

I cant use low-pass filter because the bandwidth is more than 1 octave. which pin diode parameter affect harmonics?

 

[ltrlspree]

i guess you can refer to below literature,

Avago AN1049 indicates IM3 (linearity) relation with carrier lifetime and diode resistance.
Avago AN1050 also covers many different other aspects related to Pin Diode limiter.

br