Features and overview 8bit resolution sample rates up to 8. This paper presents a high speed cmos image sensor cis with columnparallel single capacitor correlated double samplings cdss, programmable gain amplifiers pgas and single slope analogtodigital converters adcs. 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. We now consider the single slope and the dual slope adcs. The first stage single slope adc generates a 3bit data and 1 redundant. The is the basic idea behind the socalled single slope, or integrating adc. Integrating ad converter concept and single slope ad. Although capable of generating a 12bit output, it has only 10 effective bits of resolution.
Figure 1 shows a conventional cmos image sensor cis with a single slope adc ss adc. 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. Single slope adcs are very popular for a columnparallel adc in ciss because of its very simple circuit con. As a minimum, each device contains the integrator, zero crossing comparator and proc essor interface logic. Columnparallel adcs for cmos image sensors and their. With a small modification to the discharging phase of the dual slope adc, firstorder quantization noise shaping is achieved. The chapter illustrates the origin of thermal noise, flicker noise, and shot noise in circuit design. In the later half the single slope ad converter is explained using the. The main component of analog to digital converter adc single slope type is an analog unit. The pixel fpn conveys each output from the same light to the adc in the form of another voltage.
The single slope adc suffers the disadvantage of calibration drift. One form of this circuit compares a linear reference ramp to the unknown voltage input see about integrating converters and capacitors. An alternative ad conversion technique uses the single slope ad converter. There are many types of adcs employed for columnparallel architectures, such as single slope ss. 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. This paper describes a new analogtodigital converter based on the traditional dual slope adc operation. 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. Twostep single slopesar adc with error correction for. A 14bit differentialramp singleslope columnlevel adc. The proposed scheme solves the multiphase clock period matching problem in flash tdcinterpolation of ss adcs without the use of a delaylockedloop. Single slope adc with onchip accelerated continuoustime differential ramp generator for low noise columnparallel cmos image sensor author.
A prototype imager using the mrss adc architecture was realized in a 0. Single slope adc with onchip accelerated continuoustime differential ramp generator for low noise columnparallel cmos image sensor dexue zhang, rami yassine, loc truong, jeff rysinski daniel van blerkom and barmak mansoorian forza silicon corporation, 2947. The single slope adc suffers all the disadvantages of the digital ramp adc. A lowpower 12bit extended counting adc without calibration. 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. Author links open overlay panel yue chen a albert j. Here, an unknown input voltage is integrated and the value compared against a known reference value. Dexue zhang, rami yassine, loc truong, jeff rysinski, daniel van blerkom, barmak mansoorian, forza silicon corporation subject. K page 2 of 27 functional description the adc10 user module implements a single slope ad converter that generates up to a 12bit, full scale output 0 to 4095 count range. The adc10 user module implements a single slope ad converter that generates up to a 12bit, full scale output 0 to 4095 count range. There are a few ways of designing analogtodigital converters using an integrator. A columnparallel architecture has become popular for analogtodigital converter adc integration in cis, in that it features a good tradeoff among frame rate, column number, noise, and power consumption. A plurality of ramp signals are generated which define nonoverlapping subranges of the full input range. We choose a single slope adc as a candidate for interleaving because of its simplicity, linearity, lowpower operation, small area, and small input capacitance.
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. Dual slope and algorithmic jose silvamartinez single slope integrating adc precision capacitor c and current source i are required. Investigations of timeinterpolated singleslope analogto. The basic working principle of slope ad resistance measurement is the charging and discharging of a known value capacitor cm through the. Noise analysis and simulation method for a single slope adc with cds in a cmos image sensor j. Most of the water resources are under the stage of depletion. The time it takes for the integrator to trip the comparator is proportional to the unknown voltage t int v in. Ccjrootv8n5 pdf group 4 general pathology, logic and cytologic techniques free download as pdf file. Improving single slope adc and an example implemented in fpga. Article a thirdorder dt modulator using noiseshaped bi. Further resolution is achieved by averaging multiple samples.
This quantizer is used in a secondorder loop filter and results in an overall thirdorder quantization noise shaping. A prototype sensor of 256x256 pixels was realized in a 0. A singleslope 80mss adc using twostep timetodigital. Twostep single slopesar adc with error correction for cmos. Pdf design 8 bit analog unit adc integrating type single. Using the proposed columnparallel ss adc with digital cms technique, 65% random noise reduction is obtained.
It discloses two types of the popular structures, including the nyquist. Integrating adc overview aka ramp and slope adc different flavors, e. A single slope adc, particularly suitable for use in a massiveparallel adc architecture in a readout circuit of a cmos imager. This choice is nevertheless unusual because of single slope s reputation for long conversion time, normally taking 2nbits time steps, where n bits is the adc. We explain why the slightly more complicated dual slope adc is generally a better choice of adc than the single slope converter. The single slope adc suffers all the disadvantages. Single slope solar still, cfd introduction now days, lack of drinking water is majour problem in most of the countries. Measurements demonstrate that the conversion speed of an mrss adc is 3. The bms3000 single slope can be a simple one lite wide by one lite upslope opening or a complex segmented design and is available in a wide variety of pitches and framing depths from 212 to 12. This paper presents an 11bit twostep single slope successive approximation register sar adc scheme for cmos image sensor applications. Us7924207b2 single slope analogtodigital converter. A dual slope adc ds adc integrates an unknown input voltage v. Integrating and algorithmic adcs voltagetotime converters.
Download it and modify according to your values or you can use. This work presents a hybrid columnparallel timetodigitalconverter interpolated tdc single slope ss adc with a digital delay element feedback. The single and dualslope analog to digital converters. Single slope adc with onchip accelerated continuoustime differential ramp generator for low noise columnparallel cmos image sensor dexue zhang, rami yassine, loc truong, jeff rysinski, daniel van blerkom, barmak mansoorian forza silicon corporation, pasadena, ca. Lets take a look at two of them, single slope adc and deltasigma adc. An example of sh circuit is given below the role of the capacitor is to be charged. 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.
Twostep single slope adc was proposed in the prior art 5, 6 in order to solve the operation speed issue of the traditional single slope adc. Single slope adc has smaller chip area than others adcs and is suitable for columnparallel cis architectures. 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. What is more, the correlated double sampling cds operation can be used in the single slope adc to ensure uniformity between the readout columns. A singleslope 80mss adc using tw ostep timetodigital. A 10bit singleslope analogtodigital converter adc for timedelayintegration cmos image sensor was proposed. To convert analog signals to digital ones is needed to keep. The key operating principle of such structures is to translate an input voltage to a. Errors due to currentsource output impedance and leakage current comparator must handle large commonmode input. Two 8 bit successive approximation analogtodigital converters adc, an 8 bit single slope adc, and a 12 bit current mode incremental sigma delta ea adc have been designed, fabricated, and tested. A columnparallel dualgain 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. In single slope adc, using a gray code counter is a popular scheme for time digitization, in which the.
Pdf twostep single slopesar adc with error correction for. This article illustrates four techniques applied to the wellknown dualslope analogtodigital converter adc in. The singleramp singleslope srss analogtodigital converter adc is a promising candidate for columnparallel architectures. Analysis and improvement of ramp gain error in singleramp. However, multiramp signals are required for the proposed scheme and the first single slope adc must meet a full resolution noise specification. Pdf twostep single slopesar adc with error correction. An 80 mss analogtodigital converter adc based on single slope conversion is presented which utilizes a recently developed gated ring oscillator gro timetodigital converter tdc to achieve an enob of 6. Single slope conversion or integrating conversion is a classical means of implementing an analogtodigital converter adc 1, and has the advantage of having a very simple implementation with minimal analog content. The sampling rate is determined by your configuration of the clock sources and the selected parameters.
Since it consists of many pixels, pixel fpn can occur due to device mismatching errors. 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. Therefore, the columnparallel single slope architecture fig. The adc nonlinearity measurement result shows totally 0.
Single slope adc with onchip accelerated continuoustime. A novel differentialramp single slope drss structure is proposed in this work, which achieves 2x faster conversion speed and 3db higher snr performance compared with classical single slope. 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. When the ramp potential crosses the unknown input voltage a comparator changes state. Ccjrootv8n5pdf group 4 general pathology, logic and cytologic techniques free download as pdf file. By using highfactor timeinterpolation, the resolution of single slope converters can be increased without sacrificing conversion time or power. Columnparallel single slope adc with digital correlated multiple sampling for low noise cmos image sensors. 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. Single slope adc architecture the simplest form of an integrating adc uses a single slope architecture figures 1a and 1b. The proposed 12bit ec adc uses the adc and singleslope adc ss adc to convert the input voltage to the upper 4 bit and lower 8 bit, respectively. The simplest form of an integrating adc uses a single slope architecture.
One of the many ad techniques utilized in the late 50s and early 60s was the single slope integrating converter. Both adcs make use of simple opamp circuits and control logic to do most of their work. Integrating adc simulation single and dual slope using op amp. A highspeed cmos image sensor with columnparallel single. The single capacitor cds circuit has only one capacitor so that the area cds circuit is small. 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. Singleslope analogtodigital conversion technique using.
This paper presents an areaefficient and lowpower 12b successive approximation register single slope analogtodigital converter sarss adc for cmos image sensor cis applications. The time it takes for the integrator to trip the comparator is proportional to the unknown voltage tintvin. An260a 20bit1 ppm linear slopeintegrating ad converter. How analogtodigital converter adc works integrator. Columnparallel single slope adc with digital correlated. 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. Figure 1a shows the block diagram of a cis with a column parallel adc. Write the disadvantage of single slope integrator adc and. The focus of the presented investigations here is to shed light on methods in timetodigital converter interpolation of single slope adcs. The tc500 is the base 16bit max device and requires both positive and negative power supplies. This brief proposes a lowpower 12bit columnparallel extended counting analogtodigital converter ec adc without calibration for cmos image sensors. Abstract single slope adc is a common building block in many asci or fpga based frontend systems due to its simplicity, small silicon footprint, low noise interference and low power consumption.
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