AN3137 datasheet(34/42 Pages) STMICROELECTRONICS

Part #	AN3137

Description	Analog-to-digital converter on STM8L and STM8AL devices

PDF	42 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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34 / 42 page

Methods for precision improvement

AN3137

34/42

Doc ID 16983 Rev 3

Figure 19.

Parasitic capacitances of sampling switch

This charging and discharging currents (PMOS and NMOS asymmetric capacitances) can

cause charge transfer to sampling capacitor Csh.

Internal charging of sampling capacitor

It is possible that after the conversion process (successive approximation process in SAR

type of ADC) the sample and hold capacitor Csh is charged to some voltage. The reason

can be:

●

some leakage current to Csh (parasitic current inside ADC structure, see Figure 20)

●

residual charge transfer from the switches when ADC structure is switched back to

default state before next conversion

●

other reasons (related to internal ADC parasitic structures)

Figure 20.

Parasitic current example inside ADC structure

AN3137 Datasheet(PDF) 34 Page - STMicroelectronics