[SOLVED] Negative capacitor value in switched capacitor filters

[user0088]

I saw negative value for capacitors in SC filter calculation manuals. What it means? How to perform it in cadence?

Thanks.

 

[LvW]

I saw negative value for capacitors in SC filter calculation manuals. What it means? How to perform it in cadence?
Thanks.

Question: Did you see an SC circuitry that is able to act as a negative capacitor or do you speak about a simple passive element with a negative capacitance within an SC circuitry?

 

[user0088]

Question: Did you see an SC circuitry that is able to act as a negative capacitor or do you speak about a simple passive element with a negative capacitance within an SC circuitry?

I mean about "a simple passive element with a negative capacitance within an SC circuitry"

 

[varunkant2k]

Capacitance polarity is generally decided by its dc Bias.
Capacitors comes with inbuilt polarity or without polarity.

---------- Post added at 16:32 ---------- Previous post was at 16:23 ----------

Added:If you connect the meter to a component in which the voltage leads the current and ask the meter to measure the capacitance, it will give you a negative number, because current leads voltage in a (positive) capacitor, but in a negative capacitor voltage leads current. So when the meter sees that the voltage is leading current, but you've asked it to measure capacitance, it returns a negative number because only in negative capacitors does voltage lead current.

 

[LvW]

I mean about "a simple passive element with a negative capacitance within an SC circuitry"

Up to now. I never have seen an SC circuitry with negatice caps.
Please, show us the relevant page of the manual.

 

[user0088]

Up to now. I never have seen an SC circuitry with negatice caps.
Please, show us the relevant page of the manual.

Please find attached file. Capacitors' values are shown in the last page.

It is not clear, how to perform "-" value in circuit, for example in cadence.

 

[JoannesPaulus]

It is actually written in the book under the capacitor values (p. 412): "where a differential input can realize the negative capacitance."

 

[FvM]

It is not clear, how to perform "-" value in circuit, for example in cadence.

It's all about reading. The answer is stated clearly in the text, which refers to a fully differential circuit implementation.

In other words, the negative capacitance value isn't but a design formalism respectively a rule for computing and hasn't to do with real negative capacitance. In so far LvW's doubts have been approved.

 

[varunkant2k]

As far I understood, Inductor and Capacitor gives some properties ( e.g., Inductor: Voltage leads the current and capacitor reverse). If R,L or C network is working on the frequency that is more/less than Resonant frequency , the equivalent "capacitor may be positive and Inductor may be negative" or "Inductor may be positive and capacitor may be negative".

There is no polarity specification for passive elements.

 

[LvW]

It's all about reading. The answer is stated clearly in the text, which refers to a fully differential circuit implementation.
In other words, the negative capacitance value isn't but a design formalism respectively a rule for computing and hasn't to do with real negative capacitance. In so far LvW's doubts have been approved.

Yes, the negative capacitance values appear in relation to equivalent diagrams only (not in the real circuit diagram).