An answer to this calibration drift dilemma is found in a design variation called the dual slope converter. In the time domain, the analog input voltage and the output of the 1bit digitalto analog converter dac are differentiated, providing an analog voltage at x 2. Dual slope adc architecture a dual slope adc ds adc integrates an unknown input voltage vin for a fixed amount of time tint, then deintegrates tdeint using a known reference voltage vref for a variable amount of time see figure 2. The quad slope scheme results in an extremely accurate converter. The peak value attained contains the only clue but that is unknown to this type of adc. Us5321403a multiple slope analogtodigital converter. At the end of that time it is attached to the reference voltage sw1 down. Then a known reference voltage of opposite polarity is applied to the integrator and is allowed to ramp until the integrator output returns to zero. For the adcs discussed to this point, a timevarying signal was sampled or the adc operated so rapidly that, for practical purposes, the signal did not change during a single conversion. A 12bit dual slope adc of the type illustrated below timercounter enable clear clk n output bits clock control logic. Este documento foi gerado utilizando o processador pdf latex, com base no template novathesis 1. The main purpose was to construct a 16bit dual slope ad converter with an input voltage of 5v. The unknown input voltage is lead to the input of the integrator and allowed to ramp up for a defined fixed time. Pdf an adaptable 14bit dual slope adc with wide input range.
Flash type adc is based on the principle of comparing analog input voltage with a set of reference voltages. A multiple slope integrating analog todigital converter adc includes many improvements and refinements which eliminate timing and nonlinearity errors which accumulate due to a large number of switching operations that occur over an integrate cycle. From the argument there, the rc time constant of the integrator is set by v out v in trc. To convert the analog input voltage into a digital signal of nbit output, 2 n 1 comparators are required. A low power midrail dual slope analogtodigital converter for. In its basic implementation, the dual slope converter, the unknown input voltage is applied to the input of the integrator and allowed to ramp for a fixed time period the runup period. During the first slope positive slope the sampling time is a fixed value and therefore the duration gives no clue about what the input voltage is. The dual slope adc dsadc is a type of analog todigital conversion with low input bandwidths. To overcome this sensitivity to the component values, the dual slope integrating architecture is used. In operation the integrator is first zeroed close sw2, then attached to the input sw1 up for a fixed time m counts of the clock frequency 1t. Design of a moderateresolution dualslope adc using. A dual slope integrator first integrates and then disintegrates a voltage signal. Two matched current sources and two comparators are required. This adc was characterised by many metrological advantages, but could be put into practical use only in the 1970s, when the technology of semiconductor devices achieved a sufficient.
Dual slope adc architecture a dual slope adc ds adc integrates an unknown input voltage v in for a fixed amount of time t int, then deintegrates t deint using a known reference voltage v ref for a variable amount of time see. The dual slope adc is one of several devices that work in this way. Conventional dual slope integrating analog todigital converters adcs are well known to those skilled in the art, and operate by placing a charge on a capacitor associated with an operational amplifier integrator proportional to an unknown voltage to be measured charging the capacitor for a predetermined period of time, resulting in the. Dual slope type adc analogintegratedcircuits electronics tutorial.
Introduced in the 1950s, the dual slope adc architecture was truly a breakthrough in adcs for high resolution applications such as digital voltmeters, etc. A dual slope adc, on the other hand, averages together all the spikes and dips within the integration period, thus providing an output with greater noise immunity. It converts the analog input to time, and the measure the time by counting fixedfrequency pulses 3, 4. Some examples of adc usage are digital volt meters, cell phone, thermocouples, and digital oscilloscope. A video by jim pytel for renewable energy technology students at columbia gorge community college. An integrating adc is a type of analogtodigital converter that converts an unknown input voltage into a digital representation through the use of an integrator. V i control logic sha cnt 1 8 bits msbs v x c 2 i c s i 256 c 1 v t cnt 2 8 bits lsbs f clk carry. Overview of integrating adcs and the dualslope adc 22. This voltage is presented to the integrator, whose output progresses in a negative or positive direction. We now consider the single slope and the dualslope adcs. Experimental results are given to confirm the operation of the proposed adc.
It contains an integrator, a dac, a comparator, and a summing junction. Then a known reference voltage of opposite polarity is applied to the integrator and is allowed to ramp until the integrator output returns to zero the rundown period. Flash type adc data convertors analog integrated circuits. An integrating adc is a type of analog todigital converter that converts an unknown input voltage into a digital representation through the use of an integrator. Figure 5 shows the graph of dual slope integration. Successive approximation type adc analogintegrated. At the start of the conversion cycle, the capacitor is totally discharged i. It is then charged for a certain set time by the input voltage. The nature of operation of dualslope and related converters requires the instantaneous reversal of current in the integrating capacitor. The control logic resets the counter and enables the clock signal generator in order to send the clock pulses to the counter, when it is received the start commanding signal. The dualslope conversion improvement radojle radetic1, marijana pavlovkagadejev2, nikola milivojevic3 abstract. When a dual slope ad converter is used for a dvm, the counters may be decade rather than binary and the segment and digit. Dual slope adc a dual slope integrator first integrates and then disintegrates a voltage signal.
In this work, a high resolution dual slope adc, which can handle in. In the dual slope converter, an integrator circuit is driven positive and negative in alternating cycles to ramp down and then up, rather than being reset to 0 volts at the end of every cycle. The single slope adc suffers all the disadvantages. This converter is based on the same principle as the single slope converter. Frequently asked questions about data converters tutorial. When the input voltage vin equal to the voltage of the waveform, then the control circuit captures the counter value which is the digital value of the corresponding analog input value. By the set value of vref, this integrator generates a sawtooth.
Adc converter technologies may occasionally convert a spike or dip because it captures the signal repeatedly at a single point in time. Also, an indepth analysis of the integrating architecture will be discussed. Pdf dual slope adc design from power, speed and area. Like the dual slope adc, its often used in digital multimeters, panel meters, and data acquisition boards. The central comparator s current source, and a bias circuit for the discharge. Finally a comparisons against other adc architectures will aid in the understanding and selection of integrating adcs. How analogtodigital converter adc works hardware secrets. In its basic implementation, the dualslope converter, the unknown input voltage is applied to the input of the integrator and allowed to ramp for a fixed time period. Figure5 depicts block diagram of dual slope integrating type adc. The adc includes an integrator and a comparator in which an input voltage to be measured is applied to a summing node at the input of the. Apr 21, 2006 the analog modulator is somewhat similar to a dual slope adc, however using a 1bit dac as a feedback loop.
It is pretty slow, but its ability to reject highfrequency noise and fixed low frequencies such as 50 hz or 60 hz makes it. An alternative ad conversion technique uses the single slope ad converter. Hence it is called a s dual slope a to d converter. Voltage to frequency conversion adc chemistry libretexts. Dual slope adc design from power, speed and area perspectives. Handheld dmms with up to 20,000count resolution 14bits often use offtheshelf integrating adcs. The single and dualslope analog to digital converters. For n bit dual slop type of adc, vr 2 n n va total time for conversion of input va is expressed as follows. We explain why the slightly more complicated dual slope adc is. Dual slope converter timing diagram the advantage of a dual slope adc is that it is not dependent on the correction factor for the rc product. The purpose of this work was to understudy the functionalities as well as the operations of the various converters adda converters with emphasis laid on the dual slope adcs. In this type of adc converter, comparison voltage is generated by using an integrator circuit which is formed by a resistor, capacitor, and operational amplifier combination. In one direction of ramping, the integrator is driven by the positive analog input signal producing a.
The dualslope adc architecture was truly a breakthrough in adcs for high. We explain why the slightly more complicated dualslope adc is generally a better choice of adc than the single slope converter. In the dual slope module, we explained how integrators work. Oct 01, 2011 the dual slope analog todigital converter adc, invented in 1957 by gilbert, was an excellent circuit dedicated for signal conditioning and measuring purposes. The counter output will then be th digital equivalent of the input analog voltage. Aug 15, 2020 a dual slope adc, on the other hand, averages together all the spikes and dips within the integration period, thus providing an output with greater noise immunity. It is pretty slow, but its ability to reject highfrequency noise and fixed low frequencies such as. An 8 bit dual slope adc using two2 cascaded 4 bit counters. An analog todigital converter also known as an adc or an ad converter is an electronic circuit that measures a realworld signal such as temperature, pressure, acceleration, and speed and converts it to a digital representation of the signal. Pdf this article illustrates four techniques applied to the wellknown dual slope analog todigital converter adc in order to improve its speed of. Difference between adc typescounter,flash,sar,dual slope. In the dual slope converter, an integrator circuit is driven positive and negative in. The basic working principle of slope ad resistance measurement is the charging and discharging of a known value capacitor cm through the. Simple dual slope ad converter dual slope ad converter output and timing dual slope adc consider this circuit.
Explain dual slope integration type adc with the help of a. A dualslope integration based analogtodigital convertor. In the ramp techniques, the noise can cause large errors but in dual slope method the noise is averaged out by the positive and negative ramps using the process of integration. How does a sar successiveapproximationregister adc work.
Dual slope or integrating type adcwatch more videos at by. When compared to other types of adc techniques, the dual slope method is slow but is quite adequate for a digital voltmeter used for laboratory measurements. Subranging dual slope adc much faster conversion speed. International journal of computer technology and electronics.
The key advantage of this architecture over the single slope is that the final. The dual slope integration type of ad conversion is a very popular method for digital voltmeter applications. Control logic pushes the switch sw to connect to the external. Analog to digital converter how adc works with pic mcu. The errors determined during the first cycle are subtracted digitally from the result of the second cycle. It integrates an unknown voltage for a fixed time and disintegrates for variable time using a reference voltage. The dualslope adc dsadc is a type of analogtodigital conversion with low input bandwidths. In dual slope type adc, the integrator generates two different ramps, one with the known analog input voltage va and another with a known reference voltage vref. Converters adcs which can be classified according to the concept on which they.
The basic sigmadelta modulator design can be found in figure 14. In this video, the working of dual slope and single slope integrating adc is explained. An example of sh circuit is given below the role of the capacitor is to be charged. A dual slope adc ds adc integrates an unknown input voltage v. A key element of the dual slope adc is a capacitor.
Apr 27, 2019 an integrating adc dual slope adc applies the analog input voltage to the input of an integrator and allows the voltage to ramp for a fixed time period the runup period. If high resolution is desired, then the dual slope conversion technique can be employed. Sigmadelta converters are relatively inexpensive primarily because. How does it work a dual slope adc ds adc integrates an unknown input voltage v in for a fixed amount of time t int, then deintegrates t deint using a known reference voltage v ref for a variable amount of time. For the adcs discussed to this point, a timevarying signal was sampled or the adc. The conversion time is maintained constant in successive approximation type adc, and is proportional to the number of bits in the digitaloutput, unlike the counter and continuous type ad converters. Pdf working with a dualslope adc richard lao riclao. Dual slope adcs are used in applications demanding high accuracy. The improvement over the single slope converter comes from. Dual slope converter the single slope adc suffers all the disadvantages of the digital ramp adc, with the added drawback of calibration drift. Microcontrollers commonly use 8, 10, 12, or 16 bit adcs, our micro controller uses an 8 or 10 bit adc. Analog to digital conversion measurement computing.
By watching this video, you will learn the following topics. Application of adc adc are used virtually everywhere where an analog signal has to be processed, stored, or transported in digital form. Both adcs make use of simple opamp circuits and control logic to do most of their work. Integrator, comparator, clock signal generator, control logic and counter. The basic principle of this method is that the input. Single slope analog todigital ad conversion by stephen ledford csic product engineering austin, texas introduction the most common implementation for analog todigital ad conversion among motorola microcontrollers is the successive approximation sar method.
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