ADUC824 Analog Devices, ADUC824 Datasheet - Page 36

• Manufacturer Part Number: ADUC824
• Description: Precision Analog Microcontroller: 1MIPS 8052 MCU + 8kB Flash + 16/24-Bit ADC + 12-Bit DAC
• Manufacturer: Analog Devices

Specifications of ADUC824

• Mcu Core: 8052
• Mcu Speed (mips): 1
• Sram (bytes): 256Bytes
• Gpio Pins: 34
• Adc # Channels: 4

ADuC824
Figure 22 shows the frequency response of the ADC chan-
nel at the default SF word of 69 dec or 45 hex, yielding an
overall output update rate of just under 20 Hz.
It should be noted that this frequency response allows frequency
components higher than the ADC Nyquist frequency to pass
through the ADC, in some cases without significant attenuation.
These components may, therefore, be aliased and appear in-band
after the sampling process.
It should also be noted that rejection of mains-related frequency
components, i.e., 50 Hz and 60 Hz, is seen to be at level of
>65 dB at 50 Hz and >100 dB at 60 Hz. This confirms the
data sheet specifications for 50 Hz/60 Hz Normal Mode Rejec-
tion (NMR) at a 20 Hz update rate.
The response of the filter, however, will change with SF word as
can be seen in Figure 23, which shows >90 dB NMR at 50 Hz
and >70 dB NMR at 60 Hz when SF = 255 dec.
–100
–110
–120
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
0
0
0
10
10
20
20
30
30
40
FREQUENCY – Hz
FREQUENCY – Hz
40
50
50
60
60
70
70
80
80
90
100
90
100
110
Figures 24 and 25 show the NMR for 50 Hz and 60 Hz across
the full range of SF word, i.e., SF = 13 dec to SF = 255 dec.
ADC Chopping
Both ADCs on the ADuC824 implement a chopping scheme
whereby the ADC repeatability reverses its inputs. The deci-
mated digital output words from the Sinc
positive offset and negative offset term included.
As a result, a final summing stage is included in each ADC so that
each output word from the filter is summed and averaged with the
previous filter output to produce a new valid output result to be
written to the ADC data SFRs. In this way, while the ADC
throughput or update rate is as discussed earlier and illustrated
in Table VII, the full settling time through the ADC (or the time
to a first conversion result), will actually be given by 2 × t
The chopping scheme incorporated in the ADuC824 ADC results
in excellent dc offset and offset drift specifications and is
extremely beneficial in applications where drift, noise rejection,
and optimum EMI rejection are important factors.
–100
–110
–120
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
0
10
10
30
30
50
50
70
70
90
90
110
110
SF – Decimal
SF – Decimal
130
130
150 170 190 210
150 170 190 210
3
filters therefore have a
230 250
230 250
ADC
.