battery noise v.s switching regulator output ripple

Hi all,

Which noise is larger in SoCs, battery noise or switching regulator output ripple?

The switching regulator output ripple is about several tens of mV at the switching frequency. How about noise at the output of the battery, what is its amplitude and the frequency content? How the bulk capacitor near the battery and decoupling capacitors near the input of each submodule suppress the battery noise?

The output noise of battery may be very application-dependent. In what case (application) the battery noise would be smaller than the switching regulator output ripple, and in what case the battery noise would be larger?

Thanks in advance.

Battery noise is very low, and is generally white thermal noise with no specific frequency.
Here's an article on the measurement of noise with various battery chemistries.

It it unlikely that you will ever run into a situation where the battery noise is larger than the noise from a regulator.

Hi crutschow,

Thank you for your reply and the article provided, and it is very helpful.

However, it seems that the article mainly discusses the intrinsic noise of a battery, though the case for 1mA discharging current is demonstrated.

In practice, the discharging current of SoC may be very large, thereby leading to large voltage ripple on battery output (imagine the case of a 1A transient current and 100mOhm battery internal resistance, a 100mV voltage ripple would appear at the output of the battery).

I know that the bulk capacitor and the decoupling capacitors can somewhat accommodate the said transient current, and hence the voltage ripple may not be that large.

But how effective are the bulk capacitor and the decoupling capacitors, and how much voltage ripple would eventually appear at the output of the battery, is it several tens of mV, or several mV, or even smaller?

Looking forward to your reply.

Thank you.

Which noise is larger in SoCs, battery noise...

Click to expand...

Batteries do not contribute any noise per se; you can approximate a battery as a capacitor with a very large capacitance value. There will be thermal noise (1/f) and white noise (1/f°) but they are omnipresent and not a feature of the battery. White noise gives rise to "ultraviolet catastrophe" and need to be considered with care.

I see a confusion of terms. I never heard voltage ripple at the battery terminals caused by ripple current called "battery noise". Batteries have of course a frequency (and partly charging state) dependent impedance which can be measured and may be specified in data sheets.

Need to talk about specific batteries and their data.