Hello,
I am currently working on designing a low-power consumption and low phase noise cross-coupled VCO in keysight ADS. I am not getting the transient response i.e the oscillating waveform for my circuit. Could anyone please guide me through the process. I am hereby attaching my design for the reference.
You connected the base of each BJT transistor directly to the other BJT collector, which is wrong.
The DC bias of the cross-coupled VCO should look as in the schematic below:
-OSC_PORT is wrong placed, you cannot obtain any result from it..You must cut the feedback path and place it there..
-In order to get a transient simulation you have to excite the circuit temporarily to make it leave from initial condition.
-There is a good circuit in ADS examples ( keyword: CMOS VCO) , open it and inspire how a simulation setup has been prepared.
To start your circuit oscillating, it helps if there is non-symmetry between the left and right half.
This simulation seems to work okay.
The waveforms show that current flows back and forth in a loop formed by L1 L2 and the capacitor. If the capacitor is omitted then a different mode of operation takes place, namely the left half conducts while the right half is off, then its vice-versa.
I just found that your DC supply (V_DC) is placed in reverse position.
If use NPN BJTs, the negative (-) shall be connected to the ground, and positive (+) to the transistor collectors.
-OSC_PORT is wrong placed, you cannot obtain any result from it..You must cut the feedback path and place it there..
-In order to get a transient simulation you have to excite the circuit temporarily to make it leave from initial condition.
-There is a good circuit in ADS examples ( keyword: CMOS VCO) , open it and inspire how a simulation setup has been prepared.
Hi. thankyou for your reply. Could you please tell me how to excite the circuit temporarily and also there is no relevant example on cross-coupled VCO in ADS. If possible can be please provide me with the details. Thanks in advance.
Hi. I have used a small signal model instead of actual transistor just to check whether I am getting an oscillating waveform in trnsient response. But I am getting the results as follows. Can anyone please help me regarding the issue.
Hi. I am designing a cross-soupled VCO in ADS. The circuit diagram using the small signal model of transistor is as follows. While performing the transient simulation, I am not getting the oscillating waveform. Can Anyone please help me out with the issue. Thanks in advance. https://imgur.com/a/18smyoP
Hi. I am designing a cross-soupled VCO in ADS. The circuit diagram using the small signal model of transistor is as follows. While performing the transient simulation, I am not getting the oscillating waveform. Can Anyone please help me out with the issue. Thanks in advance. https://imgur.com/a/18smyoP
Small signal Models are NOT used neither in Transient nor HB analysis.
You have to read "fundamentals of simulation techniques" from different tutorials/app. notes.