Page 257 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Digital Circuits and Logic Design

Notes • Higher-resolution A/D converter using only one comparator could be constructed if a
variable reference voltage were available.
12.15 Keywords

Accuracy test: Converter output voltage when the switch is opened, the capacitor holds the voltage
level until the next sampling time the operational amplifier provides a large input impedance.

ADC0804: It is an inexpensive and very popular A/D converter which is available from a number
of different manufacturers, including National Semiconductor.

Analog to Digital converter (A/D): It is used to change the analog output signals from transducers
(measuring temperature, pressure, vibration, etc.) into equivalent digital signals.

Digital-to-analog conversion (D/A): It is a straightforward process and is considerably easier
than A/D conversion. In fact, a D/A converter is usually an integral part of any A/D converter.
Dual-Slope A/D converter: It is a popular design based on this one is called dual-slope ADC,
which solves an inherent single-slop problem called calibration drift, which leads to inaccuracy
over time because the integrator is not linked to the clock signal.

Flash converter: It remembers that three comparators were necessary for defining four ranges
in general, it can be said that 2 – 1 comparators are required to convert to a digital signal that
n
has n bits.
Free-running mode: All the logic blocks inside the dashed line or some equivalent arrangement
are frequently constructed on a single MSI chip; this chip is called a successive approximation
register (SAR).

Ladder: It is a resistive network whose output voltage is a properly weighted sum of the digital
inputs. Such a ladder, designed for 4 bits, is constructed of resistors that have only two values
and thus overcomes one of the objections to the resistive divider previously discussed.
Monotonicity test: This is so as not to discharge the capacitor appreciably and at the same time
offers gain to drive external circuits.
Steady-state: Sample-and-hold amplifier when the switch is closed, the capacitor charges to the
D/A.

Successive-approx Imation register: When dealing with conversion times this short, it is usually
necessary to take into account the other delays in the system.

1. Draw a truth table for successive approximation converter.

2. Write the Millman’s theorem and solve it.

12.16 Review Questions

1. Define variables-resistor networks.
2. Describe binary ladders. Draw the circuit diagram.
3. Describe in brief D/A converters.
4. What are A/D converters and techniques? Explain in brief.
5. Explain dual-slope A/D conversion. Draw the circuit diagram.
6. Describe A/D accuracy and resolution.

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