Simple starved ring oscillator versus fully differential type

[Junus2012]

Hello,

I would like to ask you about the difference between the simple current starved ring oscillator made of chain of inverters and the fully differential counterpart.

logically, the differential one should give some benefits otherwise why one should complicate the circuit if the simple one is doing the same job.

you can refer to the image below for your discussion

thank you very much

 

[BigBoss]

Because Differential Circuits are more Noise Tolerant and therefore most of RFIC Circuits are being as Differential Mode.

 

[Junus2012]

Because Differential Circuits are more Noise Tolerant and therefore most of RFIC Circuits are being as Differential Mode.

Thank you boss for your reply,

in my application Iam using the oscillator as a current to frequency unit for the temperature sensor circuit, will that make a difference for such a sensor to shift to the fully differential part? I mean I think noise performance will not be matter for temperature sensor so simple one should be enough?

 

[BigBoss]

Thank you boss for your reply,

in my application Iam using the oscillator as a current to frequency unit for the temperature sensor circuit, will that make a difference for such a sensor to shift to the fully differential part? I mean I think noise performance will not be matter for temperature sensor so simple one should be enough?

Noise Sensitivity is particularly important for Temperature Measurements.In fact, it depends on how much noise is injected by other circuits.If there isn't logic circuits or power systems, noise immunity can be obtained even single ended structures.But as I said, Noise Sensitivity is an important figure and it must be carefully examined.If it's a single function like Temperature Observer, yeah.. it can be less tolerant but measurement needs careful examination.

 

[sutapanaki]

Apart from noise immunity, differential ring oscillator also allows you to use even number of stages in the loop of the oscillator. With single ended inverters, the stages have to be odd number if you want to get oscillations. With differential structure, you can just get the extra inversion by crossing the outputs of one of the stages. That also means that if you use, for example 4 stages in the loop, you can get 0, 90, 180, 270 degrees phases of your oscillation frequency.

 

[Junus2012]

Apart from noise immunity, differential ring oscillator also allows you to use even number of stages in the loop of the oscillator. With single ended inverters, the stages have to be odd number if you want to get oscillations. With differential structure, you can just get the extra inversion by crossing the outputs of one of the stages. That also means that if you use, for example 4 stages in the loop, you can get 0, 90, 180, 270 degrees phases of your oscillation frequency.

Thank you Suta and Boss,

I think phase properties is good for implementing PLL, in the temperature sensor I am only using the cell as IPTAT to frequency converter so I do nothing with phase,

one point said Boss is about sensitivity to noise that can be considered,

Besides I have found that with differential scheme I can have control voltage that allow me to adjust the frequency against the shift in the PVT, which is important feature if I would like to have calibration circuit