Clocked Digital Ramp A/D Converter- Counter Ramp Analog to Digital (A/D) Conversion

The digital ramp analog to digital converter (A/D converter) is one of several circuits that can be used to change an analog signal to a digital one. Like several other analog to converters (ADCs), the digital ramp analog to digital converter includes a digital to analog converter ( DAC) in the design.


The circuit uses a single comparator, unlike some other converter designs, which utilize a large number of comparators. The converter is also known as the stairstep ramp ADC. It changes an analog signal to an 8 bit binary code.

Dynamic Latched Comparator


Analog to Digital Conversion

For an 8 bit output to be produced by another converter, for example a flash converter, as many as 255 comparators would be required. No comparator would be necessary for the all zero state in the circuit. When compared with the flash converter, the digital ramp ADC is simpler to build and less bulky in its design.


However people who choose this type of circuit for analog to digital conversion lose in terms of speed. The flash or simultaneous ADC works much faster when it is required to convert one type of signal to another.

Digital ramp ADCs are also called counter ADCs. This is because a binary counter samples the analog input in order to determine what the digital output should be. Using a counter to conduct sampling in these ADCs slows down the circuit. Every time the counter takes sample, it has to cycle through all its states until it reaches the level of the current analog input voltage.

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Mod-08 Lec-35 Dual Slopes ADC -- Design Examples

Dual Slope ADC Analog to Digital Conversion Method vs. Successive Approximation ADC

A dual slope analog to digital converter is one type of analog to digital converter (ADC). It is similar to the single slope analog to digital converter but the circuit does not only use one ramp.

Unlike some other analog to digital conversion circuits, the dual slope analog to digital converter does not rely on a digital to analog converter (DAC) as part of the circuit. The dual slope ADC uses two ramps. One ramp is the variable slope type and the other is the fixed slope type. A single integrator is used to produce both types of ramps.

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This circuit is quick but it is not the fastest type of analog to digital conversion. It is also not the most widely used method of conversion. Dual slope ADC circuits are typically used in measurement instruments such as voltmeters.

The successive approximation ADC is the second fastest method of analog to digital conversion. Like many other analog to digital converters, the successive approximation ADC utilizes a DAC. It takes in an analog signal and changes it first to a serial binary signal, then to a parallel binary output.

Apart from speed, the successive approximation analog to digital converter has another advantage. The conversion time does not change if the value of the analog input increases. Conversion time remains the same for a wide range of analog input voltages.

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