mangk
Junior Member level 1
Oscillator jitter transient simulation in spectre (Jitter varies each time)
Hi,
I am currently designing an ring oscillator of 100-200 MHz frequency, and have to measure the absolute jitter using transient simulation.
The schematic consists of a 5 stage ring oscillator and an ideal voltage source of 1 V to power the osc.
A jitter was measured using abs_jitter function, which is a built-in function in the calculator of ADE X environment.
Since the function compares and measures a switching timing difference between the osc and an ideal clock, if any noise source is not inserted in the circuit, resulting jitter value should be same, if simulated well.
However, whenever I simulate the circuit, changing some settings like simulation time or an additional circuit, resulting jitter varies drastically even though the schematic is not changed.
For example,
(Simulation 1-1) The peak to peak of the jitter (jpp) was calculated as 0.042 zs (zs: 10^-21 second)
(Simulation 1-2) However, jpp becames 400 zs when I changed simulation time to 50 us from 10 us.
(Simulation 1-3) Also, when I changed simulation time to 500 us, jpp varies to 26 as (as: 10^-18 second)
(Simulation 2) When I inserted dummy transistors in the schematic, jpp was measured 43 zs (Simulation time: 10 us)
(Simulation 3-1) When I inserted a dummy sine wave in the schematic, jpp becames to 120 zs (Amplitude: 100mV, Freq: 900 MHz). In this case, the osc frequency is increased by 60 kHz.
(Simulation 3-2) When I changed the the dummy signal frequency to 9 GHz, jpp becames to 1 fs. Also, the osc frequency was increased by 80 kHz.
Since the theoretical jitter of ideal osc is 0 s, and also since it might be difficult to output '0' by subtracting two values, the result of as to zs order might be reasonable value.
However, I think the flucturation of jpp should be checked.
Can anyone explain the situation? Why it happend and how to solve?
Help me please, thank you in advance!
Hi,
I am currently designing an ring oscillator of 100-200 MHz frequency, and have to measure the absolute jitter using transient simulation.
The schematic consists of a 5 stage ring oscillator and an ideal voltage source of 1 V to power the osc.
A jitter was measured using abs_jitter function, which is a built-in function in the calculator of ADE X environment.
Since the function compares and measures a switching timing difference between the osc and an ideal clock, if any noise source is not inserted in the circuit, resulting jitter value should be same, if simulated well.
However, whenever I simulate the circuit, changing some settings like simulation time or an additional circuit, resulting jitter varies drastically even though the schematic is not changed.
For example,
(Simulation 1-1) The peak to peak of the jitter (jpp) was calculated as 0.042 zs (zs: 10^-21 second)
(Simulation 1-2) However, jpp becames 400 zs when I changed simulation time to 50 us from 10 us.
(Simulation 1-3) Also, when I changed simulation time to 500 us, jpp varies to 26 as (as: 10^-18 second)
(Simulation 2) When I inserted dummy transistors in the schematic, jpp was measured 43 zs (Simulation time: 10 us)
(Simulation 3-1) When I inserted a dummy sine wave in the schematic, jpp becames to 120 zs (Amplitude: 100mV, Freq: 900 MHz). In this case, the osc frequency is increased by 60 kHz.
(Simulation 3-2) When I changed the the dummy signal frequency to 9 GHz, jpp becames to 1 fs. Also, the osc frequency was increased by 80 kHz.
Since the theoretical jitter of ideal osc is 0 s, and also since it might be difficult to output '0' by subtracting two values, the result of as to zs order might be reasonable value.
However, I think the flucturation of jpp should be checked.
Can anyone explain the situation? Why it happend and how to solve?
Help me please, thank you in advance!
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