MCP3911 datasheet(23/72 Pages) MICROCHIP

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DS22286A-page 23

MCP3911

4.0

TERMINOLOGY AND

FORMULAS

This section defines the terms and formulas used

throughout this data sheet. The following terms are

defined:

MCLK - Master Clock

AMCLK - Analog Master Clock

DMCLK - Digital Master Clock

DRCLK - Data Rate Clock

OSR - Oversampling Ratio

Offset Error

Gain Error

Integral Non-Linearity Error

Signal-To-Noise Ratio (SNR)

Signal-To-Noise Ratio And Distortion (SINAD)

Total Harmonic Distortion (THD)

Spurious-Free Dynamic Range (SFDR)

MCP3911 Delta-Sigma Architecture

Idle Tones

Dithering

Crosstalk

PSRR

CMRR

ADC Reset Mode

Hard Reset Mode (RESET = 0)

ADC Shutdown Mode

Full Shutdown Mode

4.1

MCLK - Master Clock

This is the fastest clock present in the device. This is

the frequency of the crystal placed at the OSC1/OSC2

inputs when CLKEXT=0 or the frequency of the clock

input at the OSC1/CLKI when CLKEXT=1. See

Figure 4-1.

4.2

AMCLK - Analog Master Clock

This is the clock frequency that is present on the analog

portion of the device, after prescaling has occurred via

the CONFIG PRE<1:0> register bits. The analog

portion includes the PGAs and the two Delta-Sigma

modulators.

FIGURE 4-1:

Clock Sub-circuitry.

4.3

DMCLK - Digital Master Clock

This is the clock frequency that is present on the digital

portion of the device, after prescaling and division by 4.

This is also the sampling frequency, that is the rate at

which the modulator outputs are refreshed. Each

period of this clock corresponds to one sample and one

modulator output. See Figure 4-1.

EQUATION 4-1:

4.4

DRCLK - Data Rate Clock

This is the output data rate, i.e., the rate at which the

ADCs output new data. Each new data is signaled by a

data ready pulse on the DR pin.

This data rate is depending on the OSR and the

prescaler with the following formula:

EQUATION 4-2:

TABLE 4-1:

MCP3911 OVERSAMPLING

RATIO SETTINGS

Config

Analog Master Clock

Prescale

PRE<1:0>

AMCLK = MCLK/ 1 (default)

AMCLK = MCLK/ 2

AMCLK = MCLK/ 4

AMCLK = MCLK/ 8

AMCLK

MCLK

PRESCALE

-------------------------------

DMCLK

AMCLK

---------------------

MCLK

PRESCALE

----------------------------------------

DRC LK

DMC LK

OSR

----------------------

AMCLK

4OSR

---------------------

MCLK

OSR

PRESCALE

-----------------------------------------------------------

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