An alternative ad conversion technique uses the singleslope ad converter. A multichannel single slope adc using tdc scheme built in a lowcost fpga device is shown in fig. An alternative ad conversion technique uses the single slope ad converter. Single slope adc architecture the simplest form of an integrating adc uses a single slope architecture figures 1a and 1b. By leveraging the linear possibly with small nonlinearity intent of analog circuits, a companion method of efficiently calculating output in piecewise linear format is developed. Pdf the main component of analog to digital converter adc single slope type is an analog unit. An863 a comparator based slope adc microchip technology. By watching this video, you will learn the following. The pixel fpn conveys each output from the same light to the adc in the form of another voltage. The time it takes for the integrator to trip the comparator is proportional to the unknown voltage tintvin. A 12bit highspeed columnparallel twostep singleslope. Paper single slope adc analog to digital converter digital.
Slope adc analogtodigital converters can be created in a variety of ways. What is more, the correlated double sampling cds operation can be used in the singleslope adc to ensure uniformity between the readout columns. A columnparallel analogtodigital converter was designed for use with cmos active pixel sensors aps. The single slope adc suffers all the disadvantages. The tc500 is the base 16bit max device and requires both positive and negative power supplies. Slope integrating adc slope integrating adc the singleslope adc suffers all the disadvantages of the digital ramp adc, with the added drawback of calibration drift. 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. This results in a residual nonlinearity well below the quantization noise. Instead of using a dac with a ramped output, we use an opamp circuit called an integrator to generate a sawtooth waveform which is then compared against the analog input by a comparator. Ht46r7xd1 ha0118e ht46r7xd1 dual slope adc dual slope adc ic operation of 16 bit dual slope adc ht46r74d1 application of dual slope adc 2002 analog devices single phase energy meter abstract. Integrating adc a complete block diagram of a dualslope. Use a resistor, capacitor, and opamp to form an integrator. Singleslope adc architecture the simplest form of an integrating adc uses a singleslope architecture figures 1a and 1b. Features and overview 8bit resolution sample rates up to 8.
This paper gives insight on the reference voltage noise origins during the continuoustime ramping phase of columnparallel cmos image sensor adcs, as well as its effect on the final. When the ramp potential crosses the unknown input voltage a comparator changes state. To understand the concepts of adcs, types of adc and its. Research article twostep single slopesar adc with error. The single and dualslope analog to digital converters. Singleslope 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 main component of analog to digital converter adc single slope type is an analog unit. Hence the high speed analog to digital converter adc integrated onchip needs to obtain the digital infrared imaging signal. In a prototype design, an 11bit adc including a upper 6bit sar adc and a lower 6bit ss adc with one redundancy bit is designed. Pdf design 8 bit analog unit adc integrating type single. A dualslope adc dsadc integrates an unknown input voltage v. Many of us consider the adc to be a mysterious device. 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 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. Measurements demonstrate that the conversion speed of an mrss adc is 3. Figure 1a shows the block diagram of a cis with a column parallel adc. Due to the advantages of the uncooled infrared focal plane array uifpa, it is widely used in various fields. Ccjrootv8n5pdf group 4 general pathology, logic and cytologic techniques free download as pdf file. Both adcs make use of simple opamp circuits and control logic to do most of their work.
Adc measurement and specification infineon technologies. At the end of this interval, a known reference voltage v r of opposite polarity is applied to the integrator. Singleslope analogtodigital conversion technique using. One of the many ad techniques utilized in the late 50s and early 60s was the singleslopeintegrating converter. The is the basic idea behind the socalled single slope, or integrating adc. A fascinating question has always been how can you convert an analog voltage to an equivalent digital word. The adc10 user module implements a single slope ad converter that generates up to a 12bit, full scale output 0 to 4095 count range. One form of this circuit compares a linear reference ramp to the unknown voltage input see about integrating converters and capacitors. Then measure the time it takes for the unknown voltage to charge the capacitor to a. Analogtodigital converter, vin, successive approximation adc, approximation adc example, average highlow. A single adc cell no control or bias circuitry objectives. This choice is nevertheless unusual because of singleslopes reputation for long conversion time, normally taking 2nbits time steps, where n.
Improving single slope adc and an example implemented in. This application note explains the theory of operation of the single slope ad, applies the principles of operation to the single slope ad on the mc68hc705jp7, and provides software examples for the control of the ad system found on this mcu. For this application note, we will build a slope converter. 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. The accelerated ramp generator is used to increase the 12bit adc conversion rate. An260a 20bit1 ppm linear slopeintegrating ad converter. The singleslope adc suffers the disadvantage of calibration drift.
The basic working principle of slope ad resistance measurement is the charging and discharging of a known value capacitor cm through the. Abstractthis paper presents a low noise cmos image sensor cis using 1012 bit configurable columnparallel single slope adcs ssadcs and digital correlated multiple sampling cms. Pdf twostep single slopesar adc with error correction. Figure 1 shows a conventional cmos image sensor cis with a singleslope adc ssadc. The sensor used is a conventional 4t active pixel with a pinnedphotodiode as photon detector. The time it takes for the integrator to trip the comparator is proportional to the unknown voltage t int v in. As a minimum, each device contains the integrator, zero crossing comparator and proc essor interface logic. We choose a singleslope adc as a candidate for interleaving because of its simplicity, linearity, lowpower operation, small area, and small input capacitance.
Two main input referred noise sources of the single slope adc include the ktc noise introduced by capacitor cos during reset phase s1 and the random noise of inverter transistors. Write the disadvantage of single slope integrator adc. We explain why the slightly more complicated dualslope adc is. In order to obtain the binary increasing slope of the ramp signals, iint is seeded by a 2bit current dac. Differential input ports are available in most fpga families today which can be used as comparators in the single slope adc. Columnparallel dualslope integrating adc pdf version. This method can also compensate for differential nonlinearity dnl in the dac used to generate the ramp. The input to the stage is assumed to be a linear ramp voltage whose range is. Because the analogtodigital converter ad converter or adc has both analog and digital functions, it is a mixedsignal device. Slope integrating adc slope integrating adc the single slope adc suffers all the disadvantages of the digital ramp adc, with the added drawback of calibration drift. 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 the runup period. Integrating adc a complete block diagram of a dualslope converter is shown below.
Therefore, the columnparallel single slope architecture fig. Investigations of timeinterpolated singleslope analogto. This paper presents an areaefficient and lowpower 12b successive approximation registersingleslope analogtodigital converter sarss adc for cmos image sensor cis applications. 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. Conversion time can vary from fast one clock period, t to slow 2no. Since the single slope adc has a large noise margin, the design complexity can be significantly relaxed. This work adopts an ultralow power single slope adc scheme as shown in figure 6. However, it generally has a long conversion time, so we propose an innovative. Here, an unknown input voltage is integrated and the value compared against a known reference value. Single slope adc architecture dual slope adc architecture.
This adc circuit behaves very much like the digital ramp adc, except that the comparator reference voltage is a smooth sawtooth waveform rather than a stairstep. Finally a comparisons against other adc architectures will aid in the understanding and selection of integrating adcs. To achieve more vivid image, the dimensions of infrared focal plane array need to be enlarged. This is done twice, once with a reference source and once with a sensor. Therefore, the columnparallel singleslope architecture fig. We propose a new single slope adc with halfperiod counter and. Single slope and dual slope adc explained duration. The analog unit is designed precisely to meet characteristics of the adc. The twostep singleslope 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 singleslope adc reading speed.
The use of a ramp with a combination of linear and quadratic portions for a singleslope adc is novel. A prototype imager using the mrss adc architecture was realized in a 0. Columnparallel single slope adc with digital correlated. When the input reaches v ref 8, the output code changes from.
The singleslope adc suffers all the disadvantages of the digital ramp adc, with the added drawback of calibration drift. Slaae10c msp430c11x electricity meters circuit diagram for an electronic meter using msp430 mcu kwh meter ic msp430 emeter slaue10b msp430 slope example. An example of sh circuit is given below the role of the capacitor is to be charged. We explain why the slightly more complicated dualslope adc is generally a better choice of adc than the singleslope converter. Since it consists of many pixels, pixel fpn can occur due to device mismatching errors. In this video, the working of dual slope and single slope integrating adc is explained. Further resolution is achieved by averaging multiple samples. 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 slope converter works by timing the rate that a capacitor charges to a specified voltage. The singleslope analogtodigital converter ssadc 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. Integrating adc overview aka ramp and slope adc different flavors, e. A columnparallel hybrid adc using sar and singleslope. One of the many interesting architectures available is the dualslope integrator.
A high resolution single slope adc with low operation. Although capable of generating a 12bit output, it has only 10 effective bits of resolution. We now consider the singleslope and the dualslope adcs. Single slope adc with onchip accelerated continuoustime. Some examples of adc usage are digital volt meters, cell phone. Third, time integration must be avoided in the computation of model outputs. Twostep single slopesar adc with error correction for. 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 kelvin divider dac intended for use as a. Analysis of the dacs linearity performance versus capacitor. Resolution the number of bits that the adc is capable of converting an analog signal. Figure 2 shows the diagram of the accelerated continuoustime differential ramp generator.