Moteur de recherche de fiches techniques de composants électroniques |
|
AD7730LBRUZ-REEL Fiches technique(PDF) 29 Page - Analog Devices |
|
AD7730LBRUZ-REEL Fiches technique(HTML) 29 Page - Analog Devices |
29 / 53 page AD7730/AD7730L –29– FASTStep Mode The second mode of operation of the second stage filter is in FASTStep mode which enables it to respond rapidly to step inputs. This FASTStep mode is enabled by placing a 1 in the FAST bit of the Filter Register. If the FAST bit is 0, the part continues to process step inputs with the normal FIR filter as the second stage filter. With FASTStep mode enabled, the second stage filter will continue to process steady state inputs with the filter in its normal FIR mode of operation. However, the part is continuously monitoring the output of the first stage filter and comparing it with the second previous output. If the difference between these two outputs is greater than a predeter- mined threshold (1% of full scale), the second stage filter switches to a simple moving average computation. When the step change is detected, the STDY bit of the Status Register goes to 1 and will not return to 0 until the FIR filter is back in the processing loop. The initial number of averages in the moving average computa- tion is either 2 (chop enabled) or 1 (chop disabled). The num- ber of averages will be held at this value as long as the threshold is exceeded. Once the threshold is no longer exceeded (the step on the analog input has settled), the number of outputs used to compute the moving average output is increased. The first and second outputs from the first stage filter where the threshold is no longer exceeded is computed as an average by two, then four outputs with an average of four, eight outputs with an average of eight, and six outputs with an average of 16. At this time, the second stage filter reverts back to its normal FIR mode of opera- tion. When the second stage filter reverts back to the normal FIR, the STDY bit of the Status Register goes to 0. Figure 15 shows the different responses to a step input with FASTStep mode enabled and disabled. The vertical axis shows the code value returned by the AD7730 and indicates the set- tling of the output to the input step change. The horizontal axis shows the number of outputs it takes for that settling to occur. The positive input step change occurs at the fifth output. In FASTStep mode, the output has settled to the final value by the eighth output. In normal mode, the output has not reached close to its final value until after the 25th output. NUMBER OF OUTPUTS 20000000 15000000 0 025 5 10 15 20 10000000 5000000 Figure 15. Step Response for FASTStep and Normal Operation In FASTStep mode, the part has settled to the new value much faster. With chopping enabled, the FASTStep mode settles to its value in two outputs, while the normal mode settling takes 23 outputs. Between the second and 23rd output, the FASTStep mode produces a settled result, but with additional noise com- pared to the specified noise level for its operating conditions. It starts at a noise level that is comparable to SKIP mode and as the averaging increases ends up at the specified noise level. The complete settling time to where the part is back within the specified noise number is the same for FASTStep mode and normal mode. As can be seen from Figure 13, the FASTStep mode gives a much earlier indication of where the output chan- nel is going and its new value. This feature is very useful in weighing applications to give a much earlier indication of the weight, or in an application scanning multiple channels where the user does not have to wait the full settling time to see if a channel has changed value. SKIP Mode The final method for operating the second stage filter is where it is bypassed completely. This is achieved by placing a 1 in the SKIP bit of the Filter Register. When SKIP mode is enabled, it means that the only filtering on the part is the first stage, sinc3, filter. As a result, the complete filter profile is as described ear- lier for the first stage filter and illustrated in Figure 10. In SKIP mode, because there is much less processing of the data to derive each individual output, the normal mode settling time for the part is shorter. As a consequence of the lesser filtering, however, the output noise from the part will be significantly higher for a given SF word. For example with a 20 mV, an SF word of 1536 and CHP = 0, the output rms noise increases from 80 nV to 200 nV. With a 10 mV input range, an SF word of 1024 and CHP = 1, the output rms noise goes from 60 nV to 200 nV. With chopping disabled and SKIP mode enabled, each output from the AD7730 is a valid result in itself. However, with chop- ping enabled and SKIP mode enabled, the outputs from the AD7730 must be handled in pairs as each successive output is from reverse chopping polarities. CALIBRATION The AD7730 provides a number of calibration options which can be programmed via the MD2, MD1 and MD0 bits of the Mode Register. The different calibration options are outlined in the Mode Register and Calibration Operations sections. A cali- bration cycle may be initiated at any time by writing to these bits of the Mode Register. Calibration on the AD7730 removes offset and gain errors from the device. The AD7730 gives the user access to the on-chip calibration registers allowing the microprocessor to read the device’s cali- bration coefficients and also to write its own calibration coeffi- cients to the part from prestored values in E2PROM. This gives the microprocessor much greater control over the AD7730’s calibration procedure. It also means that the user can verify that the device has performed its calibration correctly by comparing the coefficients after calibration with prestored values in E2PROM. The values in these calibration registers are 24 bits wide. In addition, the span and offset for the part can be adjusted by the user. REV. B |
Numéro de pièce similaire - AD7730LBRUZ-REEL |
|
Description similaire - AD7730LBRUZ-REEL |
|
|
Lien URL |
Politique de confidentialité |
ALLDATASHEET.FR |
ALLDATASHEET vous a-t-il été utile ? [ DONATE ] |
À propos de Alldatasheet | Publicité | Contactez-nous | Politique de confidentialité | Echange de liens | Fabricants All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |