Cirrus Logic CS5464 - Manual (Page 14)

CS5464
14 DS682F3
4. SIGNAL PATH DESCRIPTION
The data flow for voltage and current measurement and
the other calculations are shown in Figures
3 , 4 , and 5 .
The data flow consists of two current paths and two volt-
age paths. Both voltage paths are derived from the
same differential input pins. Each current path has its
own differential input pins.
4.1 Analog-to-Digital Converters
The voltage and temperature channels use second-or-
der delta-sigma modulators and the two current chan-
nels use fourth-order delta-sigma modulators to convert
the analog inputs to single-bit digital data streams. The
converters sample at a rate of DCLK/8. This high sam-
pling provides a wide dynamic range and simplifies an-
ti-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
S, 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
V1
OFF
V1
GAIN
I1
OFF
I1
GAIN
Figure 4. Signal Flow for V2, I2, P2, Q2 Measurements
V2
OFF
V2
GAIN
I2
OFF
I2
GAIN