ADE5166 datasheet(47/156 Pages) AD

47 / 156 page

ADE5166/ADE5169/ADE5566/ADE5569

Rev. B | Page 47 of 156

ANALOG-TO-DIGITAL CONVERSION

Each ADE5166/ADE5169/ADE5566/ADE5569 has two Σ-Δ

analog-to-digital converters (ADCs). The outputs of these ADCs

are mapped directly to waveform sampling SFRs (Address 0xE2

to Address 0xE7) and are used for 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 44 shows a first-order

Σ-Δ ADC. The converter is made up of the Σ-Δ modulator and

the digital low-pass filter (LPF).

A Σ-Δ modulator converts the input signal into a continuous

serial stream of 1s and 0s at a rate determined by the sampling

clock. In the ADE5166/ADE5169/ADE5566/ADE5569, the sam-

pling clock is equal to 4.096 MHz/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 is averaged is a meaningful result obtained.

This averaging is carried into the second part of the ADC, the

digital LPF. By averaging a large number of bits from the modu-

lator, the low-pass filter can produce 24-bit data-words that are

proportional to the input signal level.

The Σ-Δ 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) that is many times higher than the bandwidth

of interest. For example, the sampling rate in the ADE5166/

ADE5169/ADE5566/ADE5569 is 4.096 MHz/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 43).

409.6

19.2

NOISE

SIGNAL

DIGITAL

FILTER

ANTIALIASING

FILTER (RC)

SAMPLING

FREQUENCY

HIGH RESOLUTION

OUTPUT FROM DIGITAL

LPF

SHAPED

NOISE

409.6

19.2

NOISE

SIGNAL

FREQUENCY (kHz)

Figure 43. Noise Reduction Due to Oversampling and

Noise Shaping in the Analog Modulator

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 to increase the SNR by only

6 dB (one 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 Σ-Δ modulator,

the noise is shaped by the integrator, which has a high-pass type of

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 LPF. This noise shaping is shown in Figure 43.

–

INTEGRATOR

VREF

1-BIT DAC

DIGITAL

LOW-PASS

FILTER

MCLK/5

ANALOG

LOW-PASS FILTER

... 10100101 ...

LATCHED

COMPARATOR

Figure 44. First-Order

Σ-∆ ADC

ADE5166 数据表(PDF) 47 Page - Analog Devices

ADE5166 数据表(HTML) 47 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载

链接网址

ADE5166 数据表(PDF) 47 Page - Analog Devices

ADE5166 数据表(HTML) 47 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表 下载

链接网址

数据表下载