The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Simulators >> Circuit Simulators >> Build ideal fully differential amplifier using vcvs
https://designers-guide.org/forum/YaBB.pl?num=1236608035

Message started by seahs on Mar 9^th, 2009, 7:13am

Title: Build ideal fully differential amplifier using vcvs
Post by seahs on Mar 9^th, 2009, 7:13am

I saw this one on jacob's circuit design, layout and simulation(pg 841). It is using spice.

While I implemented it in sprectre. It always showed vcvs had shorted output( as shown in the graph). I simulated it anway and it didn't work.

does anybody know what the problem is?

Title: Re: Build ideal fully differential amplifier using vcvs
Post by raja.cedt on Mar 9^th, 2009, 8:16am

hi,
i don't know about cadence,but i think the problem is you have not specified the common mode voltage(you have to put separate common mode voltage source).

Thanks,
Rajasekhar.

Title: Re: Build ideal fully differential amplifier using vcvs
Post by boe on Mar 9^th, 2009, 8:26am

Seahs,
in your schematic, both sources connect to the same nets (according to net names shown); I suggest you remove net vcm and redraw it.
BOE

Title: Re: Build ideal fully differential amplifier using vcvs
Post by seahs on Mar 9^th, 2009, 10:08am

raja.cedt wrote on Mar 9^th, 2009, 8:16am:

hi,
i don't know about cadence,but i think the problem is you have not specified the common mode voltage(you have to put separate common mode voltage source).

Thanks,
Rajasekhar.

Thanks for your reply. Actually I had already specified common node voltage.
I also tried seperating them but it did not work. I think it is not a problem whether to seperate them or not. As I saw they are connected together in the jacob text book in spice.

Title: Re: Build ideal fully differential amplifier using vcvs
Post by seahs on Mar 9^th, 2009, 10:48am

I changed the vcvs_ahdl from andlLib to vcvs from analogLib, the error message disappeared. But this vcvs has lots of parameters to fill. I filled some of them and it seems still not work.

Title: Re: Build ideal fully differential amplifier using vcvs
Post by Andrew Beckett on Mar 9^th, 2009, 2:54pm

The key problem is (as was said earlier) that it appears that both of the vcvs are connected between vout_p and vout_n . It's not obvious from the schematic snippet why that is. Perhaps you could upload a simple (small) database in (say) tar.gz format with that part of the circuit, so one of us could take a look.

I don't think you need to specify a delay on vcvs - the gain should be sufficient.

Regards,

Andrew.

Title: Re: Build ideal fully differential amplifier using vcvs
Post by Geoffrey_Coram on Mar 11^th, 2009, 12:24pm

Are vout_p and vout_n netnames, or the pin names of the vcvs?

Title: Re: Build ideal fully differential amplifier using vcvs
Post by holddreams on Mar 17^th, 2009, 8:26am

Have you simulated the circuits successfully?
You can try the VCVS in the attatchment.