Design and Simulation of cross-coupled VCO in ADS

Thread Starter

rkhandare

Joined Aug 13, 2019
5
Hello everyone. I am currently designing a low power consumption and low phase noise cross-coupled VCO in ADS. But I'm not getting the oscillating waveform when performing the transient response. Can anyone please help me with the issue. Thanks in advance.
 

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Alec_t

Joined Sep 17, 2013
10,470
C1 and C2 should connect to respective transistor bases, not to each other.
If the simulator is to be believed, you've created a -333 megaVolt generator :).
 

Thread Starter

rkhandare

Joined Aug 13, 2019
5
C1 and C2 should connect to respective transistor bases, not to each other.
If the simulator is to be believed, you've created a -333 megaVolt generator :).
Thankyou for your reply. May I know how do I make the circuit oscillate after connecting the capacitors to the base of the transistors.
 

Alec_t

Joined Sep 17, 2013
10,470
I don't use ADS, but in the LTspice simulator you can specify a start-up condition, e.g. by giving one of the capacitors an initial voltage so that the circuit isn't completely symmetrical to start with.
 

Thread Starter

rkhandare

Joined Aug 13, 2019
5
I understand that. But at 1V do you have enough reverse bias on collectors
to get transistors to function as transistors, especially on c old side of operation ?


Regards, Dana.
Thanks for your reply. May I know how much supply voltage would you recommend to function the transistors properly?
 

Alec_t

Joined Sep 17, 2013
10,470
Something missing from your circuit, once you have the caps connected properly, is a respective pull-up resistor from each base to the +ve supply rail.
 

danadak

Joined Mar 10, 2018
3,627
Depends on part.

This shows at low Vce you are close to saturation, and given your Vbe is relatively
fixed this tells you what Vcb should be doing. You don't want clipping if you are trying
to amp a signal. This also effects dynamic range of signal swing at collector.

upload_2019-8-13_9-16-59.png


Regards, Dana.
 
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