500
Digital Electronics
12.10.6 Command Register, Status Register
The command register is an internal register of the ADC that can be programmed by the user to
select various modes of operation such as unipolar or bipolar mode selection, range selection, data
output format selection, etc. The status register indicates the current status of the analogue-to-digital
conversion with a ‘busy’ or ‘conversion complete’ signal.
12.10.7 Control Lines
Digital input/output pins that activate/monitor and control ADC operation are called control lines.
Some examples are chip select, write, start convert, conversion complete, etc.
Example 12.5
Determine the resolution of a 12-bit A/D converter having a full-scale analogue input voltage of 5 V.
Solution
• A 12-bit A/D converter resolves the analogue input voltage into (2
12
− 1) levels.
• The resolution = 5//2
12
− 1 = 5000//4096 − 1 = 5000/4095 = 122mV .
Example 12.6
The data sheet of a certain eight-bit A/D converter lists the following specifications: resolution eight
bits; full-scale error 0.02 % of full scale; full-scale analogue input +5 V. Determine (a) the quantization
error (in volts) and (b) the total possible error (in volts).
Solution
(a) The eight-bit A/D converter has 2
8
− 1 = 255 steps. Therefore, the quantization error = 5/255 =
5000/255 = 19.607 mV.
(b) The full-scale error = 002%offullscale = 002 × 5000/100 = 1 mV. Therefore, the total possible
error = 19607 + 1 = 20607mV .
12.11 Types of A/D Converter
Analogue-to-digital converters are often classified according to the conversion process or the conversion
technique used to digitize the signal. Based on various conversion methodologies, common types
of A/D converter include flash or simultaneous or direct-conversion A/D converters, half-flash A/D
converters, counter-type A/D converters, tracking A/D converters, successive approximation type A/D
converters, single-slope, dual-slope and multislope A/D converters and sigma-delta A/D converters.
Each of the above-mentioned types of A/D converter is described in the following paragraphs.
12.11.1 Simultaneous or Flash A/D Converters
The simultaneous method of A/D conversion is based on using a number of comparators. The number
of comparators needed for n-bit A/D conversion is 2
n
−1. One such system capable of converting an
Digital Electronics
12.10.6 Command Register, Status Register
The command register is an internal register of the ADC that can be programmed by the user to
select various modes of operation such as unipolar or bipolar mode selection, range selection, data
output format selection, etc. The status register indicates the current status of the analogue-to-digital
conversion with a ‘busy’ or ‘conversion complete’ signal.
12.10.7 Control Lines
Digital input/output pins that activate/monitor and control ADC operation are called control lines.
Some examples are chip select, write, start convert, conversion complete, etc.
Example 12.5
Determine the resolution of a 12-bit A/D converter having a full-scale analogue input voltage of 5 V.
Solution
• A 12-bit A/D converter resolves the analogue input voltage into (2
12
− 1) levels.
• The resolution = 5//2
12
− 1 = 5000//4096 − 1 = 5000/4095 = 122mV .
Example 12.6
The data sheet of a certain eight-bit A/D converter lists the following specifications: resolution eight
bits; full-scale error 0.02 % of full scale; full-scale analogue input +5 V. Determine (a) the quantization
error (in volts) and (b) the total possible error (in volts).
Solution
(a) The eight-bit A/D converter has 2
8
− 1 = 255 steps. Therefore, the quantization error = 5/255 =
5000/255 = 19.607 mV.
(b) The full-scale error = 002%offullscale = 002 × 5000/100 = 1 mV. Therefore, the total possible
error = 19607 + 1 = 20607mV .
12.11 Types of A/D Converter
Analogue-to-digital converters are often classified according to the conversion process or the conversion
technique used to digitize the signal. Based on various conversion methodologies, common types
of A/D converter include flash or simultaneous or direct-conversion A/D converters, half-flash A/D
converters, counter-type A/D converters, tracking A/D converters, successive approximation type A/D
converters, single-slope, dual-slope and multislope A/D converters and sigma-delta A/D converters.
Each of the above-mentioned types of A/D converter is described in the following paragraphs.
12.11.1 Simultaneous or Flash A/D Converters
The simultaneous method of A/D conversion is based on using a number of comparators. The number
of comparators needed for n-bit A/D conversion is 2
n
−1. One such system capable of converting an