CS5467 datasheet(14/46 Pages) CIRRUS

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CS5467

DS714F3

4. SIGNAL PATH DESCRIPTION

The data flow for voltage and current measurement and

the other calculations are shown in Figures 3, 4, and 5.

4.1 Analog-to-Digital Converters

Voltage1 channel and voltage2/temperature channel

use second-order delta-sigma modulators and the two

current channels use fourth-order delta-sigma modula-

tors to convert the analog inputs to single-bit digital data

streams. The converters sample at a rate of DCLK/8.

This high sampling provides a wide dynamic range and

simplifies anti-alias filter design.

4.2 Decimation Filters

The single-bit modulator output data is widened to 24

bits and down-sampled to DCLK/1024 with low-pass

decimation filters. These decimation filters are third-or-

der Sinc. Their outputs are passed through third-order

IIR “anti-sinc” filters, used to compensate for the ampli-

tude roll-off of the decimation filters.

4.3 Phase Compensation

Phase compensation changes the phase of current rel-

ative to voltage by changing the sampling time in the

decimation filters. The amount of phase shift is set by

bits PC[7:0] in the Configuration register (Config) for

channel 1 and bits PC[7:0] in the Control register (Ctrl)

for channel 2.

Phase compensation, PC[7:0] is a signed two’s comple-

ment binary value in the range of -1.0 to almost +1.0

output word rate (OWR) samples. For a sample rate of

4000 Hz, the delay range is ±250 uS, a phase shift of

±4.5° at 50 Hz and ±5.4° at 60 Hz. The step size would

be 0.0352° at 50 Hz and 0.0422° at 60 Hz at this sample

rate.

Figure 3. Signal Flow for V1, I1, P1, Q1 Measurements

FGA

VHPF1 IHPF1

V1GAIN

V1OFF

I1GAIN

I1OFF

Figure 4. Signal Flow for V2, I2, P2, Q2 Measurements

FGA

V2Q

V2GAIN

V2OFF

I2GAIN

I2OFF

Control Register

VHPF2 IHPF2

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