AN2688 Freescale Semiconductor / Motorola, AN2688 Datasheet - Page 8

• Manufacturer Part Number: AN2688
• Description: Implementing a 10-Bit Sigma-Delta Analog-to-Digital Converter Using the HC9S08Rx MCU Family Analog Comparator
• Manufacturer: Freescale Semiconductor / Motorola

AN2688/D
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The MCU oscillator is a traditional Pierce oscillator that can accommodate a crystal
or ceramic resonator up to 16 MHz. Resistor R
resistor such as a carbon composition resistor and it’s tolerance is not critical. C
and C
are chosen to match the requirements of a specific crystal or resonator. The crystal
manufacturer typically specifies a load capacitance that is the series combination
of C
Figure 6
to the input. Note the density of digital 1’s is proportional to the average input. If the
input is just about the internal bandgap reference voltage the output signal
oscillates at half the modulator sampling frequency. That is known as the idle
pattern.
and sinusoidal input signals, respectively.
Implementing a 10-Bit Sigma-Delta Analog-to-Digital Converter
2
Using the HC9S08Rx MCU Family Analog Comparator
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and C
Freescale Semiconductor, Inc.
should be ceramic capacitors being typically in the 5-pF to 25-pF range and
Figure 7
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illustrates the typical Σ∆ modulator output when a ramp signal is applied
3
Figure 6. First-Order Continuous-Time Σ∆ Modulator
that are usually the same size.
and
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Figure 8
Response to a Ramp Input Signal
exhibit the typical Σ∆ modulator response to triangle
3
should be a low-inductance
MOTOROLA
2