The disadvantage of a single slope integrator ADC is the calibration trift dilemma and the solution to this problem is found in a design variation called the dual-slope converter. The basic idea behind the so-called single-slope, or integrating ADC. The time it takes for the capacitor to charge up to the same voltage level as the input depends on the input signal level and the combination of -Vref, R, and C. When the capacitor reaches that voltage level, the comparator output goes high, loading the counter\’s output into the shift register for a final output. The single-slope ADC suffers all the disadvantages of the digital ramp ADC, with the added drawback of calibration drift. The time it takes for the sawtooth waveform to exceed the input signal voltage level is measured by means of a digital counter clocked with a precise-frequency square wave (usually from a crystal oscillator). The ADC’s real-time calibration scheme was proven to greatly improve the converter’s linearity and permit flexible segment setup for a wide range of possible imaging applications. Since the single-slope analog-to-digital converter with correlated double sampling (CDS/SS-ADC) in a CMOS image sensor (CIS) is composed of several operation phases in which the circuit topologies are different from each other, the noise cannot be estimated by the conventional FNS. See Answer. The simple, single-slope run-down is slow. Figure2a shows the single-slope ADCs in a CIS system consisting of a global ramp generator, comparators, and up/down counters. 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). Operation: 9. The IGFET is triggered “on” by the comparator\’s high output, discharging the capacitor back to zero volts. Then, in the other direction, with a fixed reference voltage (producing a fixed rate of output voltage change) with time measured by the same counter. After that, the spring is uncoupled from the shaft and allowed to unwind at a fixed rate, the time for it to unwind back to a relaxed state measured by a timer device. Not logged in When the comparator output is low (input voltage greater than integrator output), the integrator is allowed to charge the capacitor in a linear fashion. The only good thing to say about this circuit is that it avoids the use of a DAC, which reduces circuit complexity. © 2020 Springer Nature Switzerland AG. 195.168.10.9. Thus, the clock speed error would cancel itself out and the digital output would be exactly what it should be. The ADC … The time it takes for the integrator to trip the comparator is proportional to the unknown voltage (TINT/VIN). What is an analog-to-digital converter? This service is more advanced with JavaScript available, Digital Signal Processing Advantages: It is more accurate ADC type among all. Based Single Slope ADC For CMOS Image Sensor Column Readout @inproceedings{Guo2011BasedSS, title={Based Single Slope ADC For CMOS Image Sensor Column Readout}, author={Jia Guo}, year={2011} } Jia Guo; Published 2011; ACKNOWLEDGMENTS Since I left my country to study abroad, two years almost passed. We explain why the slightly more complicated dual-slope ADC is generally a better choice of ADC than the single-slope converter. A plurality of ramp signals are generated which define non-overlapping sub-ranges of the full input range. It utilizes a statistical approach and code-prediction methods to improve the conversion speed of standard single-slope ramp (SSR) ADC. The column-parallel single-slope ADC architecture has evolved in the last years as the preferred solution for increasing the total readout speed of CMOS imagers. Types of ADC 1. Therefore, to guarantee measurement accuracy, the reference voltage used as one of input of the comparator must be accurate and stable. Ramp type ADC 2. Experts are waiting 24/7 to provide step-by-step solutions in as fast as 30 minutes! dual slope integrating type ADC. Want to see this answer and more? check_circle Expert Answer. The sampling rate is determined by the user’s configuration of the clock sources and is limited to a maximum of 8.8 ksps. The single ADC occupies an area of 6 μm × 465 μm. The single-slope ADC suffers all the disadvantages of the digital ramp ADC, with the added drawback of calibration drift. For each ADC channel, the sub-range in which the voltage of the input signal falls is determined, and the corresponding ramp signal is selected … In single-slope integrating ADC on op-amp based circuit, called an integrator to generate a saw tooth wave form is used, instead of the use of a DAC with a ramped output. Depending on a gain value, using a signal greater than ADC saturation, a single slope ADC may be performed. Here, an unknown input voltage is integrated and the value is compared against a known reference value. Each one of … Both ADCs make use of simple op-amp circuits and control logic to do most of their work. The example shown is an N-bit ADC. and a greater amount of spring tension accumulated over that period of time. Contents show Why is ADC needed? Dual Slope type ADC 5. The time it takes for the integrator to trip the comparator is proportional to the unknown voltage (T INT /V IN). Single-Slope ADC Architecture The simplest form of an integrating ADC uses a single-slope architecture (Figures 1a and 1b). We explain why the slightly more complicated dual-slope ADC is generally a better choice of ADC than the single-slope … 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). *H Page 2 of 16 Functional Description The ADC8 User Module implements a Single Slope A/D Converter that generates an 8-bit, full scale output (0 to 255 count range). 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:”. We now consider the single-slope and the dual-slope ADCs. pp 93-97 | Another important advantage of this method is that the input signal becomes averaged as it drives the integrator during the fixed-time portion of the cycle. The most common implementation for analog-to-digital (A/D) conversion among Motorola microcontrollers is the successive approximation (SAR) method. It is shown that SSLAR ADC reduces power consumption while achieving an increased frame rate. The test sensor was fabricated in a 0.18 colonm CMOS image sensor process from TSMC. Integrator-based design (e.g., single-slope, dual-slope); Sigma-delta design (also known as delta-sigma, 1-bit ADC or oversampling ADC). Any changes in the analog signal during that period of time have a cumulative effect on the digital output at the end of that cycle. We'll assume you're ok with this, but you can opt-out if you wish. Dual-slope ADCs are used in applications demanding high accuracy. 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). The measurement cycle begins with the spring in a relaxed state. A dual-slope ADC (DS-ADC) integrates an unknown input voltage (V IN) for a fixed amount of time (T INT), then "de-integrates" (T DEINT) using a known reference voltage (V REF) for a variable amount of time. Single-Slope ADC Architecture The simplest form of an integrating ADC uses a single-slope architecture (Figures 1aand 1b). The sensor used is a conventional 4T active pixel with a pinned-photodiode as photon detector. The time it takes for the integrator to trip the comparator is proportional to the unknown voltage (T INT /V IN). 2. Cite as. The input is a voltage, with a range of 0 up to some maximum value that depends on the actual ADC. In reality, a latching circuit timed with the clock signal would most likely have to be connected to the IGFET gate to ensure full discharge of the capacitor when the comparator\’s output goes high. * 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). When the integrator output voltage falls to zero, the comparator output switches back to a low state, clearing the counter and enabling the integrator to ramp up voltage again. An ADC is represented by the schematic symbol in figure 1. The single-slope ADC suffers all the disadvantages of the digital ramp ADC, with the added drawback of calibration drift. The counter stops counting when the integrator\’s output reaches the same voltage as it was when it started the fixed-time portion of the cycle. The column-parallel single-slope ADC (SS-ADC) architecture is widely adopted for CIS because of its simplicity, low power consumption, and high linearity. Single slope ADC gives highest conversion rate. The single-slope ADC suffers all the disadvantages of the digital ramp ADC, with the added drawback of calibration drift. 즉, 공정 variation에 매우 취약하다. An answer to this calibration drift dilemma is found in a design variation called the dual-slope converter. Unable to display preview. 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. The amount of time it takes for the integrator\’s capacitor to discharge back to its original output voltage, as measured by the magnitude accrued by the counter, becomes the digital output of the ADC circuit. Over 10 million scientific documents at your fingertips. 1. However, this is not our only option. Hence it is called a s dual slope A to D converter. Here, an unknown input voltage is integrated and the value compared against a known reference value. An alternative A/D conversion technique uses the single-slope A/D converter. The proposed EQ based single-slope ADC is designed in standard 130 nm CMOS process with 3.3 V supply voltage. What is a Series-Parallel Combination Circuit? Single-slope ADC is the simplest form of an integrating ADC. Meanwhile, the counter is counting up at a rate fixed by the precision clock frequency. Want to see the step-by-step answer? I … A multi-slope run-down can speed the measurement up without sacrificing accuracy. A low-power column-parallel gain-adaptive single-slope analog-to-digital converter (ADC) for CMOS image sensors is proposed. With the digital ramp ADC, the clock frequency had no effect on conversion accuracy, only on update time. A new integrating ADC architecture called single-slope look-ahead ramp (SSLAR) ADC is introduced in this paper. This is a preview of subscription content, https://doi.org/10.1007/978-1-84800-119-0_14. If the counter\’s clock speed were to suddenly increase, this would shorten the fixed time period where the integrator “winds up” (resulting in a lesser voltage accumulated by the integrator), but it would also mean that it would count faster during the period of time when the integrator was allowed to “unwind” at a fixed rate. Since the single slope ADC has a large noise margin, the design complexity can be significantly relaxed. Not affiliated Single Slope 8-Bit ADC Document Number: 001-13249 Rev. The layout of single column parallel ADC is illustrated in Fig. Here, an unknown input voltage is integrated and the value compared against a known reference value. The basic schematic diagram is shown here: The IGFET capacitor-discharging transistor scheme shown here is a bit oversimplified. 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