A fascinating question has always been how can you convert an analog voltage to an equivalent digital word. Two principal advantages of the dualslope adc are its. A multichannel single slope adc using tdc scheme built in a lowcost fpga device is shown in fig. 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. The dualslope adc provides good accuracy and high resolution. The smallest input step that can be resolved by the adc is the lsb least significant.
Analog to digital conversion measurement computing. A single adc cell no control or bias circuitry objectives. This work adopts an ultralow power single slope adc scheme as shown in figure 6. During the 2nd slope negative slope the input voltage is disconnected and the counter begins. Difference between adc typescounter,flash,sar,dual slope. However, it generally has a long conversion time, so we propose an innovative. Adc accepts the analog signal and produces a corresponding digital output. Adc definitions and specifications application note by.
Columnparallel dualslope integrating adc pdf version. 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. To overcome this sensitivity to the component values, the dualslope integrating architecture is used. An adaptable 14bit dual slope adc with wide input range. 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. An 8 bit dual slope adc using two2 cascaded 4 bit counters. This scale factor will account for the voltage gain av, the voltage division of. A dualslope ad converter operates by charging a capacitor from the input voltage during a fixed time, then discharging it to zero. Comparision of different types of adcdigital voltmeter 7. 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. It is pretty slow, but its ability to reject highfrequency noise and fixed low frequencies such as. A prototype imager using the mrss adc architecture was realized in a 0. Integrating adcs ece614 advanced analog ic design presented by antonio oblea may 7, 2008.
The dual slope adc is an analogtodigital converter that does its conversion using. Howard austerlitz, in data acquisition techniques using pcs second. 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. The number of clock periods in the discharge time corresponds to the analog input voltage. 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. Study of various adcs and compare their performance and. We explain why the slightly more complicated dualslope adc is generally a better choice of adc than the singleslope converter. 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. The successive approximation adc has been the mainstay of data acquisition for. Both adcs make use of simple opamp circuits and control logic to do most of their work. Figure5 depicts block diagram of dual slope integrating type adc. Dual slope adc design from power, speed and area perspectives conference paper pdf available april 2009 with 2,380 reads how we measure reads.
An260a 20bit1 ppm linear slopeintegrating ad converter. 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. Pdf the dualslope conversion improvement researchgate. Numericalintegration techniques speed dualslope ad conversion figure 1. This greatly decreases the area necessary to implement the adc. Twostep single slopesar adc with error correction for. Though the operation is quite slow, it has the ability to. 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. Hope you dont mind, but ive stolen this page with a web page to pdf firefox plugin. It is pretty slow, but its ability to reject highfrequency noise and fixed low frequencies such as 50 hz or 60 hz makes it.
The dualslope adc dsadc is a type of analogtodigital conversion with low input bandwidths. The output of the adc dout is connected to the input of the dac din. Pdf the dualslope adc dsadc is a type of analogtodigital conversion with low input bandwidths. 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. Improving single slope adc and an example implemented in. An example of sh circuit is given below the role of the capacitor is to be charged. Abcs of adcs analogtodigital converter basics nicholas gray data conversion systems staff applications engineer november 24, 2003. Slope integrating adc chapter digitalanalog conversion pdf version. It is possible to avoid using a dac if we substitute an analog ramping circuit and a digital.
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. Since the single slope adc has a large noise margin, the design complexity can be significantly relaxed. The adc10, adc12, adc40 and adc42 can be connected to the pc in two ways. Michael flynn lowpower, small analogtodigital converters adcs have numerous applications in areas ranging from poweraware wireless sensing nodes for environmental. The design goals included simplicity, small size, moderate speed 10khz, current input. Also i have knicked a copy of the 8050 led display conversion, as i have one as you know. Like the dualslope adc, its often used in digital multimeters, panel meters, and data acquisition boards. Now the input is integrated for 300ms and the integrated value is 0. 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. For n bit dual slop type of adc, vr 2 n n va total time for conversion of input va is expressed as follows. One of the many interesting architectures available is the dualslope integrator. One form of this circuit compares a linear reference ramp to the unknown voltage input see about integrating converters and capacitors. What would a complete dual slope adc look like inside.
As a minimum, each device contains the integrator, zero crossing comparator and proc essor interface logic. Adc definitions and specifications application note. Single slope and dual slope adc explained duration. When the ramp potential crosses the unknown input voltage a comparator changes state.
One of the many ad techniques utilized in the late 50s and early 60s was the singleslopeintegrating converter. The peak value attained contains the only clue but that is unknown to this type of adc. A complete device list and corresponding data sheets or these products can be found at. An alternative ad conversion technique uses the singleslope ad converter. 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. Its not often someone describes this subject without making my brain hurt lol. The dual slope adc is an analogtodigital converter that does its conversion using quite low bandwidth as its input. 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.
Printer port operation when you install the application software from the pico cd, the computer will ask you which port to use. Dashed lines mean control to throw a switch or convey a pulse. The dualslope adc architecture was truly a breakthrough in adcs for high resolution. Well leave out the details of the countercontroller.
Differential input ports are available in most fpga families today which can be used as comparators in the single slope adc. 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. Thats why it is not used for the dataacquisition, but due to its good. 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. 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. The range of payload types, limited power budget, restricted fabrication options and operation in a harsh environment all combine to make. Numericalintegration techniques speed dualslope ad. Split pdfs at pages matching specific text pattern. Measurements demonstrate that the conversion speed of an mrss adc is 3. We now consider the singleslope and the dualslope adcs. Therefore, the columnparallel singleslope architecture fig. Adc converter technologies may occasionally convert a spike or dip because it captures the signal repeatedly at a single point in time.
The tc500 is the base 16bit max device and requires both positive and negative power supplies. The single and dualslope analog to digital converters. Because the analogtodigital converter ad converter or adc has both analog and digital functions, it is a mixedsignal device. Pdf dual slope adc design from power, speed and area. A columnparallel analogtodigital converter was designed for use with cmos active pixel sensors aps. Fig 4a singleslope adc architecture, fig 4b output of integrator dualslope adc architecture.