# How to measure TC in Bandgap using Cadence simulation?

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#### ccw27

##### Full Member level 5
TC in Bandgap

Given TC<20 ppm/°C, how can I measure this in cadence simulation so I know if the spec is met or not.

Thanks

#### Fom

Re: TC in Bandgap

Run DC analysis with temperature as sweeping parameter.
Using calculator select VS of bandgap voltage. Then select DERIV Special function of calculator and click plot. You will get TC. If you prefer PPM multiply it by 1000000.

### ccw27

Points: 2

#### cetc1525

##### Full Member level 3
TC in Bandgap

run DC,select temperature.then you can define your working temperature.

#### triquent

##### Full Member level 3
Re: TC in Bandgap

where to find calculator?
what is the PPM 's definition? if Temp coefficient is 50ppm/C. what is this?

Fom said:
Run DC analysis with temperature as sweeping parameter.
Using calculator select VS of bandgap voltage. Then select DERIV Special function of calculator and click plot. You will get TC. If you prefer PPM multiply it by 1000000.

#### Fom

Re: TC in Bandgap

PPM - parts per million.
50 ppm is 0.005%.
Cadence Calculator is one of the basic postprocessor tool. Look it at "Tools" menu in Analog Artist window.

kokykokykoky

### kokykokykoky

Points: 2

#### kokykokykoky

##### Newbie level 6
Re: TC in Bandgap

After following the above instructions, I got another graph plotted which is the derivative of the first. So how to get the TC in ppm/oC?

Sincere Thanks

#### aryajur

Re: TC in Bandgap

After following the above instructions, I got another graph plotted which is the derivative of the first. So how to get the TC in ppm/oC?

Sincere Thanks

As FOM mentioned above multiply your graph by a million (1000000) to get parts per million (PPM)

#### kokykokykoky

##### Newbie level 6
No, I think you do not understand my point. THe graph plotted is a range of values of TC from 0 to 100oC. So which point should I take to be the TC?

#### checkmate

It depends on your interpretation. But if I want a numerical value, this is what I use.
Given the operating temperature range and the nominal operating temperature,
TC(V/K) = (Vbg(max)-Vbg(min))/(Tmax-Tmin)
TC(ppm/K) = 10^6*(Vbg(max)-Vbg(min))/((Tmax-Tmin)*Vbg(nom))
* Note that I left out the sign, which you will have to determine from the curves.

Last edited:
vieha007Electronic

### vieha007Electronic

Points: 2

#### erikl

##### Super Moderator
Staff member
Re: TC in Bandgap

After following the above instructions, I got another graph plotted which is the derivative of the first. So how to get the TC in ppm/oC?

The plotted derivative function is $\ \frac{\partial (voltage) }{\partial (temperature) }$ in units of $\ \frac{V}{°C}\$. Divide this function by your nominal Vref - e.g. 1.22V @ 25°C - and multiply it by 1.000.000 (ppm = part per million), so you get $\ \frac{V}{°C} \times \frac{10^6}{Vref[V]) } = \ \frac{ppm}{°C}$.

So which point should I take to be the TC?
The relative temperature dependence of your ref. voltage (in $\ \frac{ppm}{°C}$) will change over the temperature range. Which value you should take depends on your specification needs: you could specify several $\ \frac{ppm}{°C}$ values for their corresponding temperature points, or you could specify min. & max values for a specified temperature range, or a mean value for such a range ± its max. deviations, e.g. for the application temperature range.