ade7763 Analog Devices, Inc., ade7763 Datasheet - Page 15

• Manufacturer Part Number: ade7763
• Description: Single-phase Active And Apparent Energy Metering Ic
• Manufacturer: Analog Devices, Inc.

–89.70
–89.75
–89.80
–89.85
–89.90
–89.95
–90.00
–90.05
–90.10
–88.0
–88.5
–89.0
–89.5
–90.0
–90.5
–1.0
–1.5
–2.0
–2.5
–3.0
–3.5
–4.0
–4.5
–5.0
–5.5
–6.0
40
40
Digital Integrator and Phase Compensator (40 Hz to 70 Hz)
Digital Integrator and Phase Compensator (40 Hz to 70 Hz)
Figure 29. Combined Phase Response of the
Figure 31. Combined Phase Response of the
Digital Integrator and Phase Compensator
Figure 30. Combined Gain Response of the
45
45
10
2
50
50
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
55
55
60
60
10
3
65
65
70
70
Rev. A | Page 15 of 56
Note that the integrator has a –20 dB/dec attenuation and
approximately a –90° phase shift. When combined with a di/dt
sensor, the resulting magnitude and phase response should be a
flat gain over the frequency band of interest. The di/dt sensor
has a 20 dB/dec gain. It also generates significant high
frequency noise, necessitating a more effective antialiasing filter
to avoid noise due to aliasing—see the Antialias Filter section.
When the digital integrator is switched off, the ADE7763 can be
used directly with a conventional current sensor such as a current
transformer (CT) or with a low resistance current shunt.
ZERO-CROSSING DETECTION
The ADE7763 has a zero-crossing detection circuit on Channel 2.
This zero crossing is used to produce an external zero-crossing
signal (ZX), which is used in the calibration mode (see the
Calibrating an Energy Meter section). This signal is also used to
initiate a temperature measurement (see the Temperature
Measurement section).
Figure 32 shows how the zero-crossing signal is generated from
the output of LPF1.
The ZX signal goes logic high upon a positive-going zero
crossing and logic low upon a negative-going zero crossing on
Channel 2. The ZX signal is generated from the output of LPF1.
LPF1 has a single pole at 140 Hz (@ CLKIN = 3.579545 MHz).
As a result, there is a phase lag between the analog input signal
V2 and the output of LPF1. The phase response of this filter is
shown in the Channel 2 Sampling section. The phase lag response
of LPF1 results in a time delay of approximately 1.14 ms
(@ 60 Hz) between the zero crossing on the analog inputs of
Channel 2 and the rising or falling edge of ZX.
V2
V2P
V2N
0.93
1.0
PGA2
Figure 32. Zero-Crossing Detection on Channel 2
1, 2, 1,
8, 16
V2
{GAIN[7:5]}
2.32° @ 60Hz
REFERENCE
LPF1
f
ADC 2
–
3dB
LPF1
= 140Hz
ZX
1
–63% TO +63% FS
CROSSING
ZERO
ADE7763
TO
MULTIPLIER
ZX