Question

QUESTION 2 [TOTAL MARKS: 25] The functional block diagram for an AD 7884 16-bit high-speed sampling ADC is shown is Figure Q2 and three pages from the AD 7884 data sheet are included at the end of the examination paper. The AD 7884 has an internal sample-and-hold and uses a two-pass flash architecture to achieve a conversion time of 5.3 ?s and maximum throughput rate of 166 kSPS. Figure Q2 2(a) [9 Marks] Explain in your own words the role and operation of the analogue input section of the AD 7884 ADC. Explain what is meant by the statement "the input resistors R1 and R2 are always connected to either virtual ground or true ground" and why this is important. Explain why there are three separate ground pins on the device (AGND, DGND and GND). 2(b) [10 Marks] The AD 7884 is described as using a two-pass flash technique. Explain what the term flash refers to here. Explain in your own words, how the overall AD 7884 converts an analogue input to a 16-bit digital output. If appropriate, use as a numerical example the analogue voltage input of 1V, that for an input range of ±3V gives rise to the ultimate 16-bit two's complement digital output of 0010 1010 1010 1011. 2(c) [6 Marks] List at least four different precautions that should be used in the design of printed circuit boards that include the typical mix of analogue and digital circuitry that are normally associated with analogue-to-digital convertors.

          QUESTION 2 [TOTAL MARKS: 25]
The functional block diagram for an AD 7884 16-bit high-speed sampling ADC is shown is Figure Q2 and three pages from the AD 7884 data sheet are included at the end of the examination paper. The AD 7884 has an internal sample-and-hold and uses a two-pass flash architecture to achieve a conversion time of 5.3 ?s and maximum throughput rate of 166 kSPS.

Figure Q2

2(a) [9 Marks]
Explain in your own words the role and operation of the analogue input section of the AD 7884 ADC. Explain what is meant by the statement "the input resistors R1 and R2 are always connected to either virtual ground or true ground" and why this is important. Explain why there are three separate ground pins on the device (AGND, DGND and GND).

2(b) [10 Marks]
The AD 7884 is described as using a two-pass flash technique. Explain what the term flash refers to here. Explain in your own words, how the overall AD 7884 converts an analogue input to a 16-bit digital output. If appropriate, use as a numerical example the analogue voltage input of 1V, that for an input range of ±3V gives rise to the ultimate 16-bit two's complement digital output of 0010 1010 1010 1011.

2(c) [6 Marks]
List at least four different precautions that should be used in the design of printed circuit boards that include the typical mix of analogue and digital circuitry that are normally associated with analogue-to-digital convertors.

QUESTION 2 [TOTAL MARKS: 25]
The functional block diagram for an AD 7884 16-bit high-speed sampling ADC is shown is Figure Q2 and three pages from the AD 7884 data sheet are included at the end of the examination paper. The AD 7884 has an internal sample-and-hold and uses a two-pass flash architecture to achieve a conversion time of 5.3 ?s and maximum throughput rate of 166 kSPS.

Figure Q2

2(a) [9 Marks]
Explain in your own words the role and operation of the analogue input section of the AD 7884 ADC. Explain what is meant by the statement "the input resistors R1 and R2 are always connected to either virtual ground or true ground" and why this is important. Explain why there are three separate ground pins on the device (AGND, DGND and GND).

2(b) [10 Marks]
The AD 7884 is described as using a two-pass flash technique. Explain what the term flash refers to here. Explain in your own words, how the overall AD 7884 converts an analogue input to a 16-bit digital output. If appropriate, use as a numerical example the analogue voltage input of 1V, that for an input range of ±3V gives rise to the ultimate 16-bit two's complement digital output of 0010 1010 1010 1011.

2(c) [6 Marks]
List at least four different precautions that should be used in the design of printed circuit boards that include the typical mix of analogue and digital circuitry that are normally associated with analogue-to-digital convertors.

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