Feddeler and bill lucas 816 bit division systems engineering austin, texas introduction this application note will help users of analogtodigital converters adc understand common terminologies used in the electronics industry to define adc operation and performance. For n bit dual slop type of adc, vr 2 n n va total time for conversion of input va is expressed as follows. Howard austerlitz, in data acquisition techniques using pcs second. 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. Split pdfs at pages matching specific text pattern. Then a known reference voltage of opposite polarity is applied to the integrator and is allowed to ramp until the integrator output returns to zero the rundown period. Numericalintegration techniques speed dualslope ad conversion figure 1. An alternative ad conversion technique uses the singleslope ad converter.
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. It is pretty slow, but its ability to reject highfrequency noise and fixed low frequencies such as. The output of the adc dout is connected to the input of the dac din. The dual slope adc is an analogtodigital converter that does its conversion using quite low bandwidth as its input. Integrating adcs ece614 advanced analog ic design presented by antonio oblea may 7, 2008. It is pretty slow, but its ability to reject highfrequency noise and fixed low frequencies such as 50 hz or 60 hz makes it.
During the 2nd slope negative slope the input voltage is disconnected and the counter begins. Fig 4a singleslope adc architecture, fig 4b output of integrator dualslope adc architecture. Since the single slope adc has a large noise margin, the design complexity can be significantly relaxed. Thats why it is not used for the dataacquisition, but due to its good. An 8 bit dual slope adc using two2 cascaded 4 bit counters. Figure5 depicts block diagram of dual slope integrating type adc. Adc scaler method the purpose of this scaler calculation is to eliminate long division in the conversion of raw adc data into a human readable decimal value using only integer math. The dualslope adc provides good accuracy and high resolution. Its not often someone describes this subject without making my brain hurt lol. When the ramp potential crosses the unknown input voltage a comparator changes state. The single and dualslope analog to digital converters. Measurements demonstrate that the conversion speed of an mrss adc is 3.
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 range of payload types, limited power budget, restricted fabrication options and operation in a harsh environment all combine to make. Comparision of different types of adcdigital voltmeter 7. A single adc cell no control or bias circuitry objectives. The smallest input step that can be resolved by the adc is the lsb least significant. One of the many interesting architectures available is the dualslope integrator. The number of clock periods in the discharge time corresponds to the analog input voltage. 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. Numericalintegration techniques speed dualslope ad. One form of this circuit compares a linear reference ramp to the unknown voltage input see about integrating converters and capacitors. A columnparallel analogtodigital converter was designed for use with cmos active pixel sensors aps. Dashed lines mean control to throw a switch or convey a pulse. The peak value attained contains the only clue but that is unknown to this type of adc.
The dualslope adc dsadc is a type of analogtodigital conversion with low input bandwidths. Also i have knicked a copy of the 8050 led display conversion, as i have one as you know. Abcs of adcs analogtodigital converter basics nicholas gray data conversion systems staff applications engineer november 24, 2003. Single slope and dual slope adc explained duration. Adc definitions and specifications application note by. Both adcs make use of simple opamp circuits and control logic to do most of their work. The tc500 is the base 16bit max device and requires both positive and negative power supplies.
An260a 20bit1 ppm linear slopeintegrating ad converter. However, it generally has a long conversion time, so we propose an innovative. This work adopts an ultralow power single slope adc scheme as shown in figure 6. This scale factor will account for the voltage gain av, the voltage division of. 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. What would a complete dual slope adc look like inside. Pdf dual slope adc design from power, speed and area. Difference between adc typescounter,flash,sar,dual slope. Adc accepts the analog signal and produces a corresponding digital output. One of the many ad techniques utilized in the late 50s and early 60s was the singleslopeintegrating converter. The dualslope conversion improvement radojle radetic1, marijana pavlovkagadejev2, nikola milivojevic3 abstract. 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.
Columnparallel dualslope integrating adc pdf version. An example of sh circuit is given below the role of the capacitor is to be charged. To overcome this sensitivity to the component values, the dualslope integrating architecture is used. We explain why the slightly more complicated dualslope adc is generally a better choice of adc than the singleslope converter. 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. A dualslope ad converter operates by charging a capacitor from the input voltage during a fixed time, then discharging it to zero.
The dual slope adc is an analogtodigital converter that does its conversion using. Twostep single slopesar adc with error correction for. We now consider the singleslope and the dualslope adcs. The successive approximation adc has been the mainstay of data acquisition for. Slope integrating adc chapter digitalanalog conversion pdf version. Study of various adcs and compare their performance and.
So for a 2v full scale the lsb or the resolution is 1mv. A complete device list and corresponding data sheets or these products can be found at. It is possible to avoid using a dac if we substitute an analog ramping circuit and a digital. Hope you dont mind, but ive stolen this page with a web page to pdf firefox plugin. Two principal advantages of the dualslope adc are its. Now the input is integrated for 300ms and the integrated value is 0. Michael flynn lowpower, small analogtodigital converters adcs have numerous applications in areas ranging from poweraware wireless sensing nodes for environmental. So far, weve only been able to escape the sheer volume of components in the flash converter by using a dac as part of our adc circuitry.
A fascinating question has always been how can you convert an analog voltage to an equivalent digital word. A dualslope adc integrates an unknown input voltage v in for a fixed amount of time, then deintegratesusing a known reference voltage v ref for a variable amount of time. Because the analogtodigital converter ad converter or adc has both analog and digital functions, it is a mixedsignal device. 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.
Analog to digital conversion measurement computing. 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. 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. Pdf the dualslope conversion improvement researchgate. Like the dualslope adc, its often used in digital multimeters, panel meters, and data acquisition boards. Though the operation is quite slow, it has the ability to. Many of us consider the adc to be a mysterious device. 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.
Adc definitions and specifications application note. A multichannel single slope adc using tdc scheme built in a lowcost fpga device is shown in fig. The adc10, adc12, adc40 and adc42 can be connected to the pc in two ways. Pdf the dualslope adc dsadc is a type of analogtodigital conversion with low input bandwidths. The dualslope adc architecture was truly a breakthrough in adcs for high resolution. A prototype imager using the mrss adc architecture was realized in a 0. Adc converter technologies may occasionally convert a spike or dip because it captures the signal repeatedly at a single point in time. This greatly decreases the area necessary to implement the adc. Therefore, the columnparallel singleslope architecture fig. Improving single slope adc and an example implemented in. An adaptable 14bit dual slope adc with wide input range. Well leave out the details of the countercontroller. Printer port operation when you install the application software from the pico cd, the computer will ask you which port to use.