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ADC0852 датащи(PDF) 11 Page - Texas Instruments |
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ADC0852 датащи(HTML) 11 Page - Texas Instruments |
11 / 22 page Functional Description (Continued) In actual practice the devices used in the ADC08524 are a simple but important expansion of the basic comparator de- scribed above As shown in Figure 4c multiple differential comparisons can be made In this circuit the feedback switch and one input switch on each capacitor (A switches) are closed in the first cycle Then the other input on each capacitor is connected while all of the first switches are opened The change in voltage at the inverter’s input as a result of the change in charge on each input capacitor (C1 C2) will now depend on both input signal differences 12 Input Sampling and Response Time The input phases of the comparator relate to the device clock (CLK) as shown in Figure 5 Because the comparator is a sampling device its response characteristics are some- what different from those of linear comparators The VIN(a) input is sampled first (CLK high) followed by VIN(b) (CLK low) The output responds to those inputs one half cycle later on CLK’s falling edge The comparator’s response time to an input step is depen- dent on the step’s phase relation to the CLK signal If an input step occurs too late to influence the most imminent comparator decision one more CLK cycle will pass before the output is correct In effect the response time for the VIN(a) input has a minimum of 1 CLK cycle a 1 mS and a maximum of 2 CLK cycles a 1 mS The VIN(b) input’s delay will range from 12 CLK cycle a 1 mS to 15 CLK cycles a 1 mS since it is sampled after VIN(a) The sampled inputs also affect the device’s response to pulsed signals As shown in the shaded areas in Figure 5 pulses that rise andor fall near the latter part of a CLK half- cycle may be ignored 13 Input Multiplexer A unique input multiplexing scheme has been utilized to pro- vide multiple analog channels with software-configurable single-ended differential or pseudo-differential operation The analog signal conditioning required in transducer-input and other types of data acquisition systems is significantly simplified with this type of input flexibility One device pack- age can now handle ground referenced inputs as well as signals with some arbitrary reference voltage On the ADC0854 the ‘‘common’’ pin (pin 6) is used as the ‘‘b’’ input for all channels in single-ended mode Since this input need not be at analog ground it can be used as the common line for pseudo-differential operation It may be tied to a reference potential that is common to all inputs and within the input range of the comparator This feature is especially useful in single-supply applications where the an- alog circuitry is biased to a potential other than ground A particular input configuration is assigned during the MUX addressing sequence which occurs prior to the start of a comparison The MUX address selects which of the analog channels is to be enabled what the input mode will be and the input channel polarity One limitation is that differential inputs are restricted to adjacent channel pairs For example channel 0 and 1 may be selected as a differential pair but they cannot act differentially with any other channel The channel and polarity selection is done serially via the DI input A complete listing of the input configurations and cor- responding MUX addresses for the ADC0852 and ADC0854 is shown in tables I and II Figure 6 illustrates the analog connections for the various input options The analog input voltage for each channel can range from 50 mV below ground to 50 mV above VCC (typically 5V) without degrading accuracy TLH5521 – 13 FIGURE 5 Analog Input Timing 10 |
Аналогичный номер детали - ADC0852 |
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Аналогичное описание - ADC0852 |
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