[ADS] Need urgent help regarding ADS. getting irregular results in S(1,1) parameters

[Fairy&cutie]

hi, i made a rectifier circuit in ads, and simulate it but my results of S(1,1) parameters are not coming good i-e the waveform is not below -10dB.

I have attached the screenshots of my circuit and result, can anybody detect the problem?

thankyou

 

[BigBoss]

"S-parameters are small signal quantities and and they are simulated with small signal equivalent circuits so they are not related to applied signal strength"

First, -30dBm is too low to activate the diodes so the circuit won't work.Diodes' turn-on values are 0.2-0.85V depending on diodes..Your voltage is 7.07mV if the source is terminated with pure 50 Ohm.
Second, s-parameters are not suitable for this kind of circuits.They are small signal parameters and all components are linearized around OP,So OP is zero, s-parameters faulty..
Third, LSSP should be used for large signal applied circuits or HB can also be used.
Transient simulation is better to observe the eventments on every net and node..

 

[Fairy&cutie]

"S-parameters are small signal quantities and and they are simulated with small signal equivalent circuits so they are not related to applied signal strength"..

hey BigBoss thanks for the reply, i found it useful, but one more question viz, i was finding the input imepedance of the circuit through S- parameters then doing matching with input source, now that u say that S- parameters are not suitable in this circuit, then what should i do to find the impedance of the load i-e diode, capacitor and resistor in parallel? and what is OP and how did you find the voltage at the diode?

will be waiting for your reply. Thanks.

 

[BigBoss]

"S-parameters are small signal quantities and and they are simulated with small signal equivalent circuits so they are not related to applied signal strength"..

hey BigBoss thanks for the reply, i found it useful, but one more question viz, i was finding the input imepedance of the circuit through S- parameters then doing matching with input source, now that u say that S- parameters are not suitable in this circuit, then what should i do to find the impedance of the load i-e diode, capacitor and resistor in parallel? and what is OP and how did you find the voltage at the diode?

will be waiting for your reply. Thanks.

The input impedance of this circuit is totally bias depended so OP of the diodes is changing with signal amplitude and this is a large amplitude therefore while s-parameters are valid for single OP they are not valid anymore for other OPs.That's why I say you " use transient or HB method".
Impedance matching is not necessary in this case because impedance is variable with OP.The most important here is to have a proper driver circuit that is able to drive this level properly to the diodes.

 

[Fairy&cutie]

ok. to get the things clear, i must tell you what this circuit actually is. basically it is a rectifier circuit which is rectifying an input signal of 2.45GHz frequency. now i can attach a bandpass filter after the source which will eliminate all the frequencies other than 2.45GHz, then a diode, a capacitor and a load resister in parallel.
now dont you think that there MUST be some matching circuit b/w bpf and diode/RC??
plus, why LSSP? i dont think that this circuit is getting large signal strength??