To overcome this sensitivity to the component values, the dual slope integrating architecture is used. This note explains the use of offset flipping for onthefly calibration of the adc. During the 2nd slope negative slope the input voltage is disconnected and the counter begins. Difference between adc typescounter,flash,sar,dual slope. A columnparallel analogtodigital converter was designed for use with cmos active pixel sensors aps. As we graph lines, we will want to be able to identify di. For the singleslope ad converter, the analog value is represented as an elapsed time and thus a 12bit resolution has 4096, or 212, discrete counts for the full range of voltage input. Adc converter technologies may occasionally convert a spike or dip because it captures the signal repeatedly at a single point in time. This work adopts an ultralow power single slope adc scheme as shown in figure 6. This is done by integrating the unknown for a predetermined length of time. A 12bit highspeed columnparallel twostep singleslope ss analogtodigital converter adc for cmos image sensors is proposed.
Both adcs make use of simple opamp circuits and control logic to do most of their work. 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. The single slope ad conversion utilizes several unique components. Measurements demonstrate that the conversion speed of an mrss adc is 3.
In the dualslope 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. Precise calibration of dualslope adcs application note maxim. The advantages of using the single slope ad converter are increased resolution, which in the case of the 68hc705jp7 is 12 bits, and the simplicity of the design. For n bit dual slop type of adc, vr 2 n n va total time for conversion of input va is expressed as follows. Twostep single slopesar adc with error correction for cmos. Dashed lines mean control to throw a switch or convey a pulse. Dualslope adc architecture a dualslope adc dsadc 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. A fascinating question has always been how can you convert an analog voltage to an equivalent digital word. If a filter was placed at the input substantial time lag due to settling requirements.
One of the most important properties of a line is its slope. A complete device list and corresponding data sheets or these products can be found at. Find the slope of a line given a graph or two points. 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 analogtodigital converters adcs provide high. The sar adc a most modern adc ic and much faster than dual slope and flash adcs since it uses a digital logic that converges the analog input voltage to the closest value. We now consider the singleslope and the dualslope adcs. The smallest input step that can be resolved by the adc is the lsb least significant.
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 and dualslope analog to digital converters. Using the dual slope ad converter function in the ht46r7xd1 rev. The tl507 is a lowcost singleslope analogto digital converter designed to convert analog inputvoltages between 0. 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. Comparision of different types of adcdigital voltmeter 7. What would a complete dual slope adc look like inside. A dual slope adc dsadc integrates an unknown input voltage vin for. A prototype imager using the mrss adc architecture was realized in a 0. With a dual slope adc you effectively get free averaging as the runup integration phase will have this effect.
It is pretty slow, but its ability to reject highfrequency noise and fixed low frequencies such as. We explain why the slightly more complicated dual slope adc is generally a better choice of adc than the single slope converter. It is pretty slow, but its ability to reject highfrequency noise and fixed low frequencies such as 50 hz or 60 hz makes it. By watching this video, you will learn the following topics. It is available as a logic design file ip, intellectual property that can be. The slope converter works by timing the rate that a capacitor charges to a specified voltage. Dual slope integrating adc the input signal is applied to an integrator. 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.
This analogtodigital converter adc has been at the heart of the digital volt meter dvm for decades. Slope adc analogtodigital converters can be created in a variety of ways. Mar 31, 2018 robert kiyosaki 2019 the speech that broke the internet keep them poor. Therefore, the columnparallel single slope architecture fig. Analogue to digital and digital to analogue converters adcs and. A single adc cell no control or bias circuitry objectives. We explain why the slightly more complicated dualslope adc is generally a better choice of adc than the singleslope converter. The tc500 is the base 16bit max device and requires both positive and negative power supplies. Follow 7 views last 30 days marceljoseph etoga on 10 oct 20. The peak value attained contains the only clue but that is unknown to this type of adc. The advantages of using the singleslope ad converter are increased resolution, which in the case of the 68hc705jp7 is 12 bits, and the simplicity of the design. The purpose of this article is to consider current commercial adc and dac. By watching this video, you will learn the following.
Abstract a lowpower singleslope analogtodigital converter. Dual slope converter an integrating adc in which the unknown. The single slope adc suffers all the disadvantages. 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. Thetc500a510514 family are precision analog front ends that implement dual slope ad converters having a maximum resolution of 17 bits plus sign. However, to obtain the increase in resolution, the rate of conversion is increased when compared to the sar ad. A dualslope adc, on the other hand, averages together all the spikes and dips within the integration period, thus providing an output with greater noise immunity. The dual slope converter is the most commonly used of the charge balance type. A 12bit highspeed columnparallel twostep singleslope. However, it generally has a long conversion time, so we propose an innovative. At the end of t 1, the tcu restarts the internal timer to measure the elapsed time period t 2.
Precise calibration of dualslope adcs application note. 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. Dmm basics dualslope adc posted on february 8, 20 by modemhead this is the first in a series of posts looking at how a digital multimeter actually works. 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. Dual slope adcs are used in applications demanding high accuracy.
The main purpose was to construct a 16bit dual slope ad converter with an input voltage of 5v. Hence, at the end of t 1, the integrator output will be positive, and the output of the comparator v c will be 1. Maxim design support technical documents tutorials ad and da. Well leave out the details of the countercontroller. An answer to this calibration drift dilemma is found in a design variation called the dualslope converter. Ss adc is presented that uses an ultralowpower reference current to achieve scription. 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. This is a decided disadvantage because most real world signals require some smoothing. Therefore, the columnparallel singleslope architecture fig. Aug 08, 2014 one of the many interesting architectures available is the dual slope integrator. It is unsure why americans use the letter m to represent slope. The dualslope adc dsadc is a type of analogtodigital conversion with low input bandwidths. 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 dualslope conversion improvement radojle radetic1, marijana pavlovkagadejev2, nikola milivojevic3 abstract.
Dual slope converter an integrating adc in which the. An answer to this calibration drift dilemma is found in a design variation called the dual slope converter. However, multiramp signals are required for the proposed scheme and the first single slope adc must meet a full resolution noise specification. This is done twice, once with a reference source and once with a sensor.
The time on the dial is proportional to the input voltage. 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. Twostep single slopesar adc with error correction for. Since v c is high, the polarity of kx is taken as positive, and the tcu sets both s1 and s2 in. Analogtodigital converter design guide highperformance, standalone ad converters for a variety of embedded systems applications design ideas in this guide are based on many of microchips adc products. I have read up about the integrator circuit and think i know how it works.
One of the many interesting architectures available is the dualslope integrator. This greatly decreases the area necessary to implement the adc. An example of sh circuit is given below the role of the capacitor is to be charged. The dual slope adc dsadc is a type of analogtodigital conversion with low input bandwidths. The design goals included simplicity, small size, moderate speed 10khz, current input. Analog to digital converter adc is an electronic integrated circuit used to convert the analog signals such as voltages to digital or binary form consisting of 1s and 0s. Unlike a dualslope,this converter has no inherent noise rejection capability.
Dualslope adc architecture a dualslope adc dsadc 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 figure 2. Ha0118e introduction this example shows how the internal dual slope adc function in the ht46r7xd1 device is used. A quadslope adc multiplier article pdf available in international journal of electronics 552. A block diagram of the circuit figure 1 includes a single primary li cell, a millivoltoutput bridge sensor, a differential amplifier, and the dualslope adc, plus correction circuitry for offset, zero, and span. The singleslope ad conversion utilizes several unique components. Write the disadvantage of single slope integrator adc. Since the single slope adc has a large noise margin, the design complexity can be significantly relaxed. Slope comes from the latin root slupan, for the word slip. 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. You can think of this method as a stop watch of sorts. A dualslope adc dsadc 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.
As a minimum, each device contains the integrator, zero crossing comparator and proc essor interface logic. Figure5 depicts block diagram of dual slope integrating type adc. Ein analogdigitalumsetzer ist ein elektronisches gerat, bauelement oder teil eines. The proposed adc employs a single ramp voltage and multiple reference voltages, and the conversion is divided into coarse phase and fine phase to. This circuit consists of a comparator, output latches, successive approximation register sar and da converter. It tells how steep a linear function is when graphed.
The output is also extremely simple, just a pulse that needs to be timed which can be done with even the simplest micro controllers. Simply count the time it takes for the integrator voltage to ramp back down to zero volts. Using the dual slope ad converter function in the ht46r7xd1. Just a few basic components constructs this basic adc implementation. 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. Mohanet al novel dualslope resistancetodigital converter 1015 shown in fig.
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. We now consider the single slope and the dual slope adcs. A dualslope adc dsadc 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. An260a 20bit1 ppm linear slopeintegrating ad converter. Write the disadvantage of single slope integrator adc and. 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. To overcome this sensitivity to the component values, the dualslope integrating architecture is used. For this application note, we will build a slope converter. Therefore, an 8bit ad converter has 256, or 28, discrete levels for the range of analog values to be converted. The timer is used to set a charge up time after which the same timer is used to. This clever analogtodigital converter adc has been at the heart of the digital volt meter dvm for decades.
Columnparallel dualslope integrating adc pdf version. An integrating adc in which the unknown signal is converted to a proportional time interval, which is then measured digitally. The basic function of an adc is to convert a voltage applied to its input into a number with a. Thus vi rises linearly with a slope of iic vairc, as indicated in fig. With a dualslope adc you effectively get free averaging as the runup integration phase will have this effect. The ex input signal is directly coupled to the comparator input with no filtering.
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