The programmable current source feeds an external capacitor to generate the ramp voltage used in the conversion. Dual slope is a spinoff of the simplest types of analog todigital conversion, as shown in the demonstration analog todigital conversion algorithm with a single slope. The circuit shown to the right is an example of a multi slope rundown. The accurate correspondence of this adc s output with its input is dependent on the voltage slope of the integrator being matched to the counting rate of the counter the clock frequency. A columnparallel dual gain single slope adc comprises an input for receiving a signal vin, a sampleandhold stage which receives vin and outputs sampled signal vin,samp, a comparator, a counter, and a ramp generator which generates highgain hg and lowgain lg ramps, with the ratio of the lg ramp slope to the hg ramp slope being greater than 1. A columnparallel analogtodigital converter was designed for use with cmos active pixel sensors aps. Single slope adc architecture the simplest form of an integrating adc uses a single slope architecture figures 1a and 1b.
The single slope adc suffers the disadvantage of calibration drift. Dual slope adc working of dual slope adc is discussed in this video. Difference between adc typescounter,flash,sar,dual slope. The single and dual slope analog to digital converters. Dual slope a to d converter this lecture is dealing with the second type of integrating ad converter dual slope. A dualslope integration based analog todigital convertor hasan krad department of computer science and engineering, college of engineering, qatar university, p. Then a reference input is switched to the integrator, which integrates down from the level determined by the unknown until the starting level is reached. As a minimum, each device contains the integrator, zero. 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. Thetc500a510514 family are precision analog front ends that implement dual slope ad converters having a maximum resolution of 17 bits plus sign. The dual slopeconverter features high accuracy, since its performance is independenl of the exact values of rand e. The time it takes for the integrator to trip the comparator is proportional to the unknown voltage t int v in.
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. Each analog input channel is multiplexed to a single analog input source to be converted by means of a slope conversion method using a single precision comparator. An example of sh circuit is given below the role of the capacitor is to be charged. Explain dual slope integration type adc with the help of a. The basic working principle of slope ad resistance measurement is the charging and discharging of a known value capacitor cm through the.
Dec 11, 2014 if the slope here means the slope of the transfer characteristic, it would be closely related to the linearity, gain and monotonous characteristic of the adc. One form of this circuit compares a linear reference ramp to the unknown voltage input see about integrating converters and capacitors. The tc510 is a precision analog front end dual slope ad converter having a maximum resolution of 17 bits plus sign. Lets take a look at two of them, single slope adc and deltasigma adc. Us10205463b1 dualgain singleslope adc with digital cds. Singleslope 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. 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. Columnparallel dual slope integrating adc pdf version. We explain why the slightly more complicated dual slope adc is generally a better choice of adc than the single slope converter.
An alternative ad conversion technique uses the single slope ad converter. Although single slope integratorswere used in early ads and voltmeters their dependence on an integrating capacitor for stability was considered an intolerable weakness. At the end of that time it is attached to the reference voltage sw1 down. It is pretty slow, but its ability to reject highfrequency noise and fixed low frequencies such as. Single slope adc architecture dual slope adc course hero. The single slope adc suffers all the disadvantages of the digital ramp adc, with the added drawback of calibration drift. Singleslope analogtodigital conversion technique using. Jagadeesh kumar, member, ieee abstracta dualslope resistancetodigital dsrdc converter that accepts the resistance of a single element resistivetype sensor as input and provides a direct digital output proportional. Integrating or dual slope dacs the dual slope are very precise, but slow converters that use counters to generate the output. 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. Feb 24, 2014 a video by jim pytel for renewable energy technology students at columbia gorge community college. The tc514 adds both a negative power supply converter and a 4input. Mar 22, 2014 the single slope analogtodigital converter ss adc is the most commonly used columnlevel adc for highspeed industrial, complementary metaloxide semiconductor cmosbased xray image sensors because of its small chip area the width of a pixel, its simple circuit structure, and its low power consumption. Msp430 mcus without an integrated adc module, resistive elements still can be precisely measured with the onchip comparator and timer using single slope analog todigital ad conversion technique.
This page covers difference between various adc types including block diagram, equation etc. This note explains the use of offset flipping for onthefly calibration of the adc. It has the added advantage of maintaining accuracy in a noisy environment. Twostep single slopesar adc with error correction for cmos. Write the disadvantage of single slope integrator adc and. An260a 20bit1 ppm linear slopeintegrating ad converter. Analogtodigital conversion algorithm with a single slope. Dual slope or integrating type adc watch more videos at lecture by. With the advent of the advanced technology and the need for more. A block diagram of the circuit figure 1 includes a single primary li cell, a millivoltoutput bridge sensor, a differential amplifier, and the dual slope adc, plus correction circuitry for offset, zero, and span. What is more, the correlated double sampling cds operation can be used in the single slope adc to ensure uniformity between the readout columns. The dual slope adc is an analogtodigital converter that does its conversion using quite low. Vin dual slope integration good accuracy without extreme requirements on components. 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.
Dual slope adc design from power, speed and area perspectives. Pdf the dualslope conversion improvement researchgate. If the output of the counter is a binary number, it will therefore be a binary representation of the input voltage. Errors due to currentsource output impedance and leakage current comparator must handle large commonmode input. In a single slope adc, there is a tradeoff between. But another strategy is to do signal averaging in but another strategy is to do signal averaging in single slope adc how will we know dual slope adc tutorial all frequencies of. The proposed adc consists of an analog part including an integrator and a comparator and a digital part including a controller, counter and 8bit register. A single adc cell no control or bias circuitry objectives. Conventional twostep adc for cmos image sensor requires full resolution noise performance in the first stage single slope adc, leading to high power consumption and large chip area. This architecture is simple, has a voltage output and is inherently monotonic even if a resistor is. Single slope operates by using a capacitor to create a linear voltage ramp to compare the actual signal to, and then recording the time it takes the linear ramp to reach the. Integrating adc overview aka ramp and slope adc different flavors, e.
The kelvin divider as we mentioned in the section on sampling theory, the output of a dac for an all 1s code is 1 lsb below the reference, so a. Dual slope and algorithmic jose silvamartinez single slope integrating adc precision capacitor c and current source i are required. Columnparallel single slope adc with digital correlated. Discussions include single, dual and multislope conversions. The single slope adc suffers all the disadvantages. It covers counter type adc,parallel comparator flash adc, sarsuccessive approximation register type adc,sigma delta adc, dual slope integrating type adc etc. First, a linear voltage ramp is created by the analog. Dual slope converter an integrating adc in which the. To minimize cost one of the design goals was to devise techniques requiring a minimum of precision parts. As shown in figures 410a and 410b, the voltage to be measured v x is input to an integrator, charging the capacitor for a fixed time interval t 1, which corresponds to a certain number of clock cycles. Msp430 mcus without an integrated adc module, resistive elements still can be precisely measured with the onchip comparator and timer using single slope analogtodigital ad conversion technique. The particular methodology shown here is called single slope and is one of the simplest kinds of conversion. The counter is likewise divided into two sections, one for the msbs and one for the lsbs. This article illustrates four techniques applied to the wellknown dual slope analogtodigital converter adc in.
Simple dual slope ad converter dual slope ad converter output and timing dual slope adc consider this circuit. One method of addressing the digital ramp adcs shortcomings. A plurality of ramp signals are generated which define nonoverlapping subranges of the full input range. Single slope analogtodigital ad conversion by stephen ledford csic product engineering austin, texas introduction the most common implementation for analogtodigital ad conversion among motorola microcontrollers is the successive approximation sar method. The analog todigital convertor attempts to convert the analog signal into digital bits in a twostep process. Pdf the dualslope adc dsadc is a type of analogtodigital conversion with low input bandwidths. A columnparallel dual gain single slope adc comprises an input for receiving a signal vin, a sample and hold stage which receives vin and outputs sampled signal vin,samp, a comparator, a counter, and a ramp generator which generates highgain hg and lowgain lg ramps, with the ratio of the lg ramp slope to the hg ramp slope being greater than 1. Flash adc is the fastest of all da converters and uses 2n1 comparators. Dual slope converter the singleslope adc suffers all the disadvantages of the digital ramp adc, with the added drawback of calibration drift.
Case 3 a businessman is talking to his sales office in rome. For each adc channel, the subrange in which the voltage of the input signal falls is determined, and the corresponding ramp signal is selected for use in the a. A low power midrail dual slope analogtodigital converter for. Precise calibration of dualslope adcs application note maxim.
The dual slope adc dsadc is a type of analog todigital conversion with low input bandwidths. Impact of dual slope path loss on user association in hetnets. The key advantage of this architecture over the single slope is. Adc converter technologies may occasionally convert a spike or dip because it captures the signal repeatedly at a single point in time. The simplest form of an integrating adc uses a single slope architecture. The tc500 is the base 16bit max device and requires both positive and negative power supplies.
We now consider the single slope and the dual slope adcs. These adcs are integrating type adc, meaning that they use. Single slope adc architecture dual slope adc architecture. The single and dualslope analog to digital converters. Another common adc is the dual slope converter, which relies on integration. Integrating and algorithmic adcs voltagetotime converters. These adcs are integrating type adc, meaning that they use the integrator for the conversion.
Jagadeesh kumar, member, ieee abstracta dualslope resistancetodigital dsrdc converter that accepts the resistance of a singleelement resistivetype sensor as input and provides a direct digital output proportional. Integrating adcs ece614 advanced analog ic design presented by antonio oblea may 7, 2008. 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. The component mismatch in the dac limits its linearity and therefore of the adc to around 12bits. The advent of the dual slope converter see about integrating converters and capacitors solved the problem of integrating capacitor. Therefore, the columnparallel single slope architecture fig. The twostep single slope adc can meet the needs of the high frame rate cmos image sensor for the circuit reading speed, and make up for the shortcoming of the single slope adc reading speed. An integrating adc in which the unknown signal is converted to a proportional time interval, which is then measured digitally. Precise calibration of dualslope adcs application note. The key advantage of this architecture over the singleslope is that the final.
Dual slope integrating adc the input signal is applied to an integrator. A dual slope adc ds adc integrates an unknown input voltage v. This paper presents an 11bit twostep single slope successive approximation register sar adc scheme for cmos image sensor applications. Us7924207b2 single slope analogtodigital converter. One of the many ad techniques utilized in the late 50s and early 60s was the single slope integrating converter. Ccjrootv8n5 pdf group 4 general pathology, logic and cytologic techniques free download as pdf file. The dual slope adc dsadc is a type of analogtodigital conversion with low input bandwidths. 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. This tradeoff between conversion time and for these op amps to save supply current. 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.
Here, an unknown input voltage is integrated and the value compared against a known reference value. The dual slope integration type of ad conversion is a very popular method for digital voltmeter applications. It is pretty slow, but its ability to reject highfrequency noise and fixed low frequencies such as 50 hz or 60 hz makes it. The smallest input step that can be resolved by the adc is the lsb least significant. 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. Dual range adc block diagram figure 5 shows the block diagram of a dual range adc. The conclusion of the study showed the efficiency of the dual slope adc as compared to other adcs, most especially the single slope adc keywords dual slope, adc, 8 bit, counter, cascaded 4 bit. The accurate correspondence of this adcs output with its input is dependent on the voltage slope of the integrator being matched to the counting rate of the counter the clock frequency. This adc circuit behaves very much like the digital ramp adc, except that the comparator reference voltage is a smooth saw tooth waveform rather than a stair step. A dualslope adc dsadc integrates an unknown input voltage v. A dualslope integration based analogtodigital convertor.
Dual slope integrating adc dual slope integrating adc. The following article explains how integrating adcs work. As a minimum, each device contains the integrator, zero crossing comparator and proc essor interface logic. The dualslope conversion improvement radojle radetic1, marijana pavlovkagadejev2, nikola milivojevic3 abstract. How analogtodigital converter adc works integrator. There are a few ways of designing analog todigital converters using an integrator.
The singleslope adc suffers all the disadvantages of the digital ramp adc, with the added drawback of calibration drift. International journal of computer technology and electronics. Selecting ad converters university of colorado boulder. This is done by integrating the unknown for a predetermined length of time. If the slope here means the slope of the transfer characteristic, it would be closely related to the linearity, gain and monotonous characteristic of the adc. The dualslope adc architecture was truly a breakthrough in adcs for high resolution. The dualslope adc dsadc is a type of analogtodigital conversion with low input bandwidths.
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