MCP3464 datasheet(27/108 Pages) MICROCHIP

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DS20006180D-page 27

MCP3461/2/4

4.0

TERMINOLOGY AND

FORMULAS

This section defines the terms and formulas used

throughout this document. The following terminology is

defined:

• MCLK – Master Clock

• AMCLK – Analog Master Clock

• DMCLK – Digital Master Clock

• DRCLK – Data Rate Clock

• OSR – Oversampling Ratio

• Offset Error

• Gain Error

• Integral Nonlinearity Error (INL)

• Signal-to-Noise Ratio (SNR)

• Signal-to-Noise and Distortion Ratio (SINAD)

• Total Harmonic Distortion (THD)

• Spurious-Free Dynamic Range (SFDR)

• MCP3461/2/4 Delta-Sigma Architecture

• Power Supply Rejection Ratio (PSRR)

• Common-Mode Rejection Ratio (CMRR)

• Digital Pins’ Output Current Consumption

FIGURE 4-1:

System Clock Details.

4.1

MCLK – Master Clock

This is either the master clock frequency at the MCLK

input pin when an external clock source is selected or

the internal clock frequency when an internal clock is

selected.

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 PRE[1:0] bits.

EQUATION 4-1:

ANALOG MASTER CLOCK

4.3

DMCLK – Digital Master Clock

This is the clock frequency that is present on the digital

portion of the device. This is also the sampling fre-

quency or the rate at which the modulator outputs are

refreshed. Each period of this clock corresponds to one

sample and one modulator output. See Equation 4-2.

EQUATION 4-2:

DIGITAL MASTER CLOCK

4.4

DRCLK – Data Rate Clock

This is the output data rate in Continuous mode, which

is the rate at which the ADC outputs new data. Each

new data are signaled by a data ready pulse on the IRQ

pin. This data rate depends on the OSR and the

prescaler, as shown in Equation 4-3.

EQUATION 4-3:

DATA RATE

Since this is the output data rate, and since the

decimation filter is a sinc (or notch) filter, there is a

notch in the filter transfer function at each integer

multiple of this rate.

MCLK

Pad

1/OSR

Intern al Oscillator

MCLK

Multiplexer

OU T

PRESCALE

1/4

AMCLK

DMCLK

DRCLK

Clock Divider

OSR[3:0]

PRE[1:0]

CLK_SEL[1]

AMCLKOUT

CLK_SEL[1] =

CLK_SEL[1:0] =

AMCLK

MCLK

Prescale

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

DMCLK

AMCLK

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

MCLK

4 Prescale



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

DRCLK

DMCLK

OSR

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

AMCLK

4OSR



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

MCLK

4 OSR Prescale



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

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