Fig 4a singleslope adc architecture, fig 4b output of integrator dualslope adc architecture. A quadslope adc multiplier article pdf available in international journal of electronics 552. So, realworld signals must be converted into digital, using a circuit called adc analog todigital converter, before they can be. Dashed lines mean control to throw a switch or convey a pulse. Many of us consider the adc to be a mysterious device. So for a 2v full scale the lsb or the resolution is 1mv. 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. 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. Adc converter technologies may occasionally convert a spike or dip because it captures the signal repeatedly at a single point in time. The single slope adc suffers all the disadvantages. 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. Study of various adcs and compare their performance and. We choose a single slope adc as a candidate for interleaving because of its simplicity, linearity, lowpower operation, small area, and small input capacitance. 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.
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. 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. An example of sh circuit is given below the role of the capacitor is to be charged. 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. Both adcs make use of simple opamp circuits and control logic to do most of their work. A columnparallel analogtodigital converter was designed for use with cmos active pixel sensors aps. Measurements demonstrate that the conversion speed of an mrss adc is 3. Columnparallel dualslope integrating adc pdf version.
It can, however, be considered very simply to be the instrument that it is. 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. 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. The control logic resets the counter and enables the clock signal generator in order to send the clock pulses to the counter.
The singleslope adc suffers all the disadvantages of the digital ramp adc, with the added drawback of calibration drift. It could also be a convert start or encode command which would happen once per conversion. Ee247 lecture 19 university of california, berkeley. The purpose of this work was to understudy the functionalities as well as the operations of the various converters adda converters with emphasis laid on the dual slope adcs. 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. A fascinating question has always been how can you convert an analog voltage to an equivalent digital word. The output of the adc dout is connected to the input of the dac din. Well leave out the details of the countercontroller. The main purpose was to construct a 16bit dual slope ad converter with an input voltage of 5v. It is possible to avoid using a dac if we substitute an analog ramping circuit and a digital. The sampling clock input is a critical function in an adc and a source of some confusion. 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. Integrator, comparator, clock signal generator, control logic and counter. To overcome this sensitivity to the component values, th e dual slope integrating architecture is used.
This greatly decreases the area necessary to implement the adc. In a dualslopeconverter the output represents the ratio of the time required to integrate the unknown voltage for a fixed time and then, using a reference voltage of opposing polarity, measures the amount of time required to get back to the original starting point see about integrating converters and capacitors. Slope integrating adc chapter digitalanalog conversion pdf version. One of the many interesting architectures available is the dualslope integrator. Precise calibration of dualslope adcs application note. A single adc cell no control or bias circuitry objectives. 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. Welcome to the adc adview 2 thank you for choosing the adc adview 2 modular diagnostic station for accurate spotchecking of vital signs. Icl7106 internal structure half flash adc application of dual slope adc dual slope adc an2094 app2094 icl7106 max153 text. Now the input is integrated for 300ms and the integrated value is 0. It has been optimized for lowest code size, fitting in a lowcost 0. 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.
Adc is a software calendar with appointments notes, tasks, alarms and contacts that provides seamless integration and interactivity with the desktop background. This frequency would typically be several times higher than the sampling rate of the converter. Therefore, the columnparallel single slope architecture fig. One of the many ad techniques utilized in the late 50s and early 60s was the singleslopeintegrating converter. Then a reference input is switched to the integrator, which integrates down from the level determined by the unknown until the starting level is. How analogtodigital converter adc works hardware secrets. After a predetermined amount of time t, a reference voltage having opposite polarity is applied to the integrator. The output is also extremely simple, just a pulse that needs to be timed which can be done with even the simplest micro controllers. Adc architectures slope type converters successive approximation flash. 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. This note explains the use of offset flipping for onthefly calibration of the adc. Its not often someone describes this subject without making my brain hurt lol. Improving single slope adc and an example implemented in fpga.
An alternative ad conversion technique uses the singleslope ad converter. Single slope and dual slope adc explained duration. We choose a singleslope adc as a candidate for interleaving because of its simplicity, linearity, lowpower operation, small area, and small input capacitance. An integrating adc in which the unknown signal is converted to a proportional time interval, which is then measured digitally. In the dualslope converter, an integrator circuit is driven. A prototype imager using the mrss adc architecture was realized in a 0. A multichannel single slope adc using tdc scheme built in a lowcost fpga device is shown in fig. 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. For n bit dual slop type of adc, vr 2 n n va total time for conversion of input va is expressed as follows. Adc architectures university of california, berkeley. This choice is nevertheless unusual because of singleslopes reputation for long conversion time, normally taking 2nbits time steps, where n bits is the adc resolution. Adc converters adc architectures and design continued flash adc and its sources of error.
Now the input is integrated for 300ms and the integrated. An alternative ad conversion technique uses the single slope ad converter. Because the analogtodigital converter ad converter or adc has both analog and digital functions, it is a mixedsignal device. Fig 4a single slope adc architecture, fig 4b output of integrator dual slope adc architecture. 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. Adc architectures slope type converters successive approximation flash timeinterleaved parallel converter folding. The dualslope adc dsadc is a type of analogtodigital conversion with low input bandwidths. One form of this circuit compares a linear reference ramp to the unknown voltage input see about integrating converters and capacitors.
We now consider the singleslope and the dualslope adcs. A complete device list and corresponding data sheets or these products can be found at. Comparision of different types of adc digital voltmeter 7. With a dualslope adc you effectively get free averaging as the runup integration phase will have this effect. What would a complete dual slope adc look like inside. Thetc500a510514 family are precision analog front ends that implement dual slope ad converters having a maximum resolution of 17 bits plus sign. 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. The smallest input step that can be resolved by the adc is the lsb least significant. The tc500 is the base 16bit max device and requires both positive and negative power supplies.
As a minimum, each device contains the integrator, zero crossing comparator and proc essor interface logic. The single and dualslope analog to digital converters. When the ramp potential crosses the unknown input voltage a comparator changes state. The adview 2 is designed to be simple and efficient to use, and features. To get started, download project files and a code example. The dualslope conversion improvement radojle radetic1, marijana pavlovkagadejev2, nikola milivojevic3 abstract. Abcs of adcs analogtodigital converter basics nicholas gray data conversion systems staff applications engineer november 24, 2003. Singleslope analogtodigital conversion technique using. In the dual slope converter, an integrator circuit is driven. Dual slope adc the dual, dchop dsrr dopao figure 5 dsrc dscc dual slope adc internal structure diagram 6, dual slope adc control registers using the ht46r71d1 as an example. This is done by integrating the unknown for a predetermined length of time. An260a 20bit1 ppm linear slopeintegrating ad converter. We explain why the slightly more complicated dualslope adc is generally a better choice of adc than the singleslope converter.
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. The design goals included simplicity, small size, moderate speed 10khz, current input. A dual slope 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. Improving single slope adc and an example implemented in.
It is pretty slow, but its ability to reject highfrequency noise and fixed low frequencies such as 50 hz or 60 hz makes it. Dual slope converter timing diagram the advantage of a dual slope adc is that it is not dependent on the correction factor for the rc product. Precise calibration of dualslope adcs application note maxim. Two principal advantages of the dualslope adc are its. Hope you dont mind, but ive stolen this page with a web page to pdf firefox plugin. The implementation presented demonstrates the slope ad conversion resistance measurement using the onchip comparator and timer of the msp430 mcus. One of the many ad techniques utilized in the late 50s and early 60s was the single slope integrating converter. Therefore, the columnparallel singleslope architecture fig.
With a dual slope adc you effectively get free averaging as the runup integration phase will have this effect. Dual slope converter an integrating adc in which the. 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 resolution. Integrating adcs ece614 advanced analog ic design presented by antonio oblea may 7, 2008. The dualslope adc dsadc is a type of analogtodigital conversion which converts an unknown input voltage u x into a digital representation through the use of an integrator, fig. Also i have knicked a copy of the 8050 led display conversion, as i have one as you know. A contemporary, compact design an integrated handle for easy mobility automatic bp checks. 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 adcr and adcd registers are, 1 cost effective device. However, it generally has a long conversion time, so. Figure5 depicts block diagram of dual slope integrating type adc. The dual slope adc dsadc is a type of analogtodigital conversion which converts an unknown input voltage u x into a digital representation through the use of an integrator, fig. The accurate correspondence of this adcs 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. Differential input ports are available in most fpga families today which can be used as comparators in the single slope adc. The design goals included simplicity, small size, moderate speed 10khz, current input, and reasonable.
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