ade7169f16 Analog Devices, Inc., ade7169f16 Datasheet - Page 42

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

ADE7169F16
In addition to the PGA, Channel 1 also has a full-scale input
range selection for the ADC. The ADC analog input range
selection is also made using the gain register—see Figure 17. As
mentioned previously, the maximum differential input voltage is
0.5 V.
ANALOG TO DIGITAL CONVERSION
The ADE7169F16 has two sigma-delta Analog to Digital
Converters (ADC). The outputs of these ADCs are mapped
directly to waveform sampling SFRs (address 0xE2 to 0xE7) and
are used for the energy measurement internal digital signal
processing. In PSM1 (Battery mode)and PSM2 (Sleep mode),
the ADCs are powered down to minimize power consumption.
For simplicity, the block diagram in Figure 18 shows a first-
order -∆ ADC. The converter is made up of the -∆
modulator and the digital low-pass filter.
LOW-PASS FILTER
PGA 2 GAIN SELECT
000 = x 1
001 = x 2
010 = x 4
011 = x 8
100 = x 16
ANALOG
R
C
CURRENT AND VOLTAGE CHANNELS PGA CONTROL
7
0
Figure 17. ADE7169F16 Analog Gain Register
* REGISTER CONTENTS
V1N
V1P
V
SHOW POWER-ON DEFAULTS
7
0
IN
6
0
Figure 16. PGA in current channel
+
6
0
Figure 18. First-Order -∆ ADC
5
0
–
5
0
INTEGRATOR
GAIN REGISTER*
GAIN[7:0]
4
0
V
4
0
REF
1-BIT DAC
3
0
3
0
K
.....10100101.....
MCLK/5
+
–
V
2
0
2
0
IN
LATCHED
COMPARATOR
1
0
1
0
RESERVED
GAIN (K)
SELECTION
0
0
0
0
PGA 1 GAIN SELECT
000 = x 1
001 = x 2
010 = x 4
011 = x 8
100 = x 16
ADDR:
1BH
LOW-PASS
DIGITAL
FILTER
Rev. PrD | Page 42 of 140
24
SIGNAL
SIGNAL
A -¨ modulator converts the input signal into a continuous
serial stream of 1s and 0s at a rate determined by the sampling
clock. In the ADE7169F16, the sampling clock is equal to
MCLK/5. The 1-bit DAC in the feedback loop is driven by the
serial data stream. The DAC output is subtracted from the input
signal. If the loop gain is high enough, the average value of the
DAC output (and therefore the bit stream) can approach that of
the input signal level. For any given input value in a single
sampling interval, the data from the 1-bit ADC is virtually
meaningless. Only when a large number of samples are averaged
is a meaningful result obtained. This averaging is carried out in
the second part of the ADC, the digital low-pass filter. By
averaging a large number of bits from the modulator, the low-
pass filter can produce 24-bit data-words that are proportional
to the input signal level.
The -∆ converter uses two techniques to achieve high
resolution from what is essentially a 1-bit conversion technique.
The first is oversampling. Oversampling means that the signal is
sampled at a rate (frequency), which is many times higher than
the bandwidth of interest. For example, the sampling rate in the
ADE7169F16 is MCLK/5 (819.2 kHz) and the band of interest is
40 Hz to 2 kHz. Oversampling has the effect of spreading the
quantization noise (noise due to sampling) over a wider
bandwidth. With the noise spread more thinly over a wider
bandwidth, the quantization noise in the band of interest is
lowered — see Figure 19. However, oversampling alone is not
efficient enough to improve the signal-to-noise ratio (SNR) in
the band of interest. For example, an oversampling ratio of 4 is
required just to increase the SNR by only 6 dB (1 bit). To keep
the oversampling ratio at a reasonable level, it is possible to
shape the quantization noise so that the majority of the noise
lies at the higher frequencies. In the -∆ modulator, the noise is
shaped by the integrator, which has a high-pass-type response
for the quantization noise. The result is that most of the noise is
at the higher frequencies where it can be removed by the digital
low-pass filter. This noise shaping is shown in Figure 19.
NOISE
NOISE
0
0
Figure 19. Noise Reduction Due to Oversampling and
OUTPUT FROM DIGITAL
Noise Shaping in the Analog Modulator
2
2
HIGH RESOLUTION
DIGITAL
Preliminary Technical Data
FILTER
LPF
FREQUENCY (kHz)
FREQUENCY (kHz)
ANTILALIAS
FILTER (RC)
409.6
409.6
SHAPED
NOISE
FREQUENCY
SAMPLING
819.2
819.2
02875-0-047