ade7169f16 Analog Devices, Inc., ade7169f16 Datasheet - Page 43

• Manufacturer Part Number: ade7169f16
• Description: Single-phase Energy Measurement Ic With 8052 Mcu, Rtc And Lcd Driver
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
Anti-aliasing Filter
Figure 18 also shows an analog low-pass filter (RC) on the input
to the modulator. This filter is present to prevent aliasing.
Aliasing is an artifact of all sampled systems. Aliasing means
that frequency components in the input signal to the ADC,
which are higher than half the sampling rate of the ADC,
appear in the sampled signal at a frequency below half the
sampling rate. Figure 20 illustrates the effect. Frequency
components (arrows shown in black) above half the sampling
frequency (also know as the Nyquist frequency, i.e., 409.6 kHz)
are imaged or folded back down below 409.6 kHz. This happens
with all ADCs regardless of the architecture. In the example
shown, only frequencies near the sampling frequency, i.e., 819.2
kHz, move into the band of interest for metering, i.e., 40 Hz to 2
kHz. This allows the use of a very simple LPF (low-pass filter)
to attenuate high frequency (near 819.2 kHz) noise, and
prevents distortion in the band of interest. For conventional
current sensors, a simple RC filter (single-pole LPF) with a
corner frequency of 10 kHz produces an attenuation of
approximately 40 dB at 819.2 kHz — see Figure 20. The 20 dB
per decade attenuation is usually sufficient to eliminate the
effects of aliasing for conventional current sensors. However, for
a di/dt sensor such as a Rogowski coil, the sensor has a 20 dB
per decade gain. This neutralizes the –20 dB per decade
attenuation produced by one simple LPF. Therefore, when using
a di/dt sensor, care should be taken to offset the 20 dB per
decade gain. One simple approach is to cascade two RC filters
to produce the –40 dB per decade attenuation needed.
0.5V, 0.25V,
0.125V, 62.5mV,
31.3mV
I
0V
V1
IBP
*WHEN DIGITAL INTEGRATOR IS ENABLED, FULL-SCALE OUTPUT DATA IS ATTENUATED
IAP
IN
DEPENDING ON THE SIGNAL FREQUENCY BECAUSE THE INTEGRATOR HAS A –20dB/DECADE
FREQUENCY RESPONSE. WHEN DISABLED, THE OUTPUT WILL NOT BE FURTHER ATTENUATED.
ANALOG
INPUT
RANGE
PGA1
PGA1
x1, x2, x4,
x8, x16
{GAIN[2:0]}
REFERENCE
ADC
ADC
Figure 21. ADC and Signal Processing in Current Channel
HPF
HPF
Rev. PrD | Page 43 of 140
0xD70A3E
0x28F5C2
0x000000
INTEGRATOR*
DIGITAL
MODE1[5]
ADC Transfer Function
Both ADCs in the ADE7169F16 are designed to produce the
same output code for the same input signal level. With a full-
scale signal on the input of 0.5 V and an internal reference of
1.2 V, the ADC output code is nominally 2,684,354 or 28F5C2h.
The maximum code from the ADC is ±4,194,304; this is
equivalent to an input signal level of ±0.794 V. However, for
specified performance, it is recommended that the full-scale
input signal level of 0.5 V not be exceeded.
Current Channel ADC
Figure 21 shows the ADC and signal processing chain for the
current channel. In waveform sampling mode, the ADC outputs
a signed twos complement 24-bit data-word at a maximum of
25.6 kSPS (MCLK/160). With the specified full-scale analog
input signal of 0.5 V (or 0.25 V or 0.125 V—see the Analog
Inputs section) the ADC produces an output code that is
approximately between 0x28F5C2 (+2,684,354d) and
0xD70A3E (–2,684,354d)—see Figure 21.
0
Figure 20. ADC and Signal Processing in current channel Outline Dimensions
dt
CURRENT CHANNEL
WAVEFORM
DATA RANGE
2
FREQUENCIES
IMAGE
FREQUENCY (kHz)
ALIASING EFFECTS
409.6
50Hz
0xCBD330
0x342CD0
0xD487B0
0x2B7850
0x000000
0x000000
60Hz
CURRENT RMS (IRMS)
CALCULATION
WAVEFORM SAMPLE
REGISTER
ACTIVE AND REACTIVE
POWER CALCULATION
CURRENT CHANNEL
WAVEFORM
DATA RANGE AFTER
INTEGRATOR (50Hz)
CURRENT CHANNEL
WAVEFORM
DATA RANGE AFTER
INTEGRATOR (60Hz)
ADE7169F16
819.2
FREQUENCY
SAMPLING