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Crystal oscillator: How to simulate the equivalent negative

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mikechiang

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Crystal oscillator: How to simulate the equivalent negative resistance?
Hi ... I am designing crystal oscillator
anyone can tell me how to simulate the equivalent negative resistance using
Hspice?
Thanks....
 

do ac open loop simulation using .net and plot zout
 

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    mikechiang

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Re: Crystal oscillator: How to simulate the equivalent negat

I don't understand you.. do you need to design the crystal Osc. itself or design using crystal Osc. ? if it is the first .. sorry i can't help but need you to tell me how to do this to get new knowledge .. thnak you
 

Re: Crystal oscillator: How to simulate the equivalent negat

Thanks arsenal's help
but my simulation result is wrong
because the simulation result zout(r) is positive not negative
my simulation file as following

vdd vdd 0 3.3
vss vss 0 0
mp1 vdd in out vdd hp w=10u l=1u m=1
mn1 out in vss vss hn w=5u l=1u m=1
*rf in out 10MEG
c1 in vss 10p
c2 out vss 10p
vin in vss ac=1
.ac lin 10 30MEG 35MEG
.net v(out) vin
.probe ac zout(i) zout(r) zout(m)


do I make something wrong ...

thanks arsenal's help
 

when do an open-loop simulation, oscillator model should be included, ? If only use the inverter without oscillator model, we can get the gain of the inverter not open-loop gain. ?
 

Re: Crystal oscillator: How to simulate the equivalent negat

mikechiang said:
Thanks arsenal's help
but my simulation result is wrong
because the simulation result zout(r) is positive not negative
my simulation file as following

vdd vdd 0 3.3
vss vss 0 0
mp1 vdd in out vdd hp w=10u l=1u m=1
mn1 out in vss vss hn w=5u l=1u m=1
*rf in out 10MEG
c1 in vss 10p
c2 out vss 10p
vin in vss ac=1
.ac lin 10 30MEG 35MEG
.net v(out) vin
.probe ac zout(i) zout(r) zout(m)


do I make something wrong ...

thanks arsenal's help
Click to expand...

hi mikechiang, surely it will be a negative resistance because of the inverter and i think first u should add the parallel capacitance in the crystal model in the netlist and as to the .net, i think it should be a one port circuit, u may try add an ac current and try the one-port .net analysis, anyway, u can calculate the negative resistance using small signal model and it should be like -gm/(w*w*c1*c2)
 

Re: Crystal oscillator: How to simulate the equivalent negat

Now I have a stupid question:
in the netlist you did not have a xtal subcircuit. Xtal itself should be connected between in and out nodes.

So what is really open loop for this circuit - you have loop created by the resistor (10Meg) and then loop done byt the XTAl between in and out nodes.

I would love to learn how to simulate that circuit too...
 
the feedback resistor is for setting the operating point of the inverters and it is very large,
the open loop gain can be get by cutting the feedback path of the xtal, and at the resonant freq the open loop gain will be high(>1) otherwise it will be very small;
since mikechiang only wanna simulate the negative resistor, the xtal can be removed
 
Hi friends
I have a basic question..why do u want to include crystal's shunt capacitance while measuring negative resistance.

my second clarification is:
I need to run an ac analysis & at the frequency of interest I need to checkout impedance of input source. am I right ?
& then I can tune my load cap to get a negative resistance X5 times of ESR of crystal so as to meet safety margin requirements.

please clarify.

~sunny
 

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