acquisition system are specified as a complete function, which removes the necessity of calculating performance from a collection of individual worst case device specifications. A complete monolithic system should achieve a higher performance at much lower cost than would be possible with a system built up from discrete functions. Furthermore, system calibration is easier and in fact many monolithic DASs are self calibrating With these high levels of integration, it is both easy and inexpensive to make many of the parameters of the device programmable Parameters which can be programmed include gain, filter cutoff frequency, and even ADC resolution and conversion time, as well as the obvious digitalmuX functions of input channel selection, output data format, and unipolar/bipolar range The AD7890 is an example of a highly integrated monolithic data acquisition system. It has 8 multiplexed input channels, a SHA, an internal voltage reference and a fast 12-bit ADC. Input scaling allows up to 10v inputs when operating on a single +5V supply. Its block diagram is shown in Figure 6. 12, and key specifications are summarized in Figure 6. 13. Both AC and dc parameters are fully specified simplifying the preparation of an error budget, and three types are available with three different standard input ranges AD7890-10±10V AD7890-50to5V AD7890-20to+25V AD7890 8-CHANNEL. 12-BIT 100kSPS COMPLETE DATA ACQUISITION SYSTEM °AEPm 2k9厂+25 REFERENCE AD7890 ○cexr OUTPUT CONTROL REGISTER AGND AGND DGND W0Ki丽smu NO SCALING ON AD7890-2 Figure 6.12
1 1 acquisition system are specified as a complete function, which removes the necessity of calculating performance from a collection of individual worst case device specifications. A complete monolithic system should achieve a higher performance at much lower cost than would be possible with a system built up from discrete functions. Furthermore, system calibration is easier and in fact many monolithic DASs are self calibrating. With these high levels of integration, it is both easy and inexpensive to make many of the parameters of the device programmable. Parameters which can be programmed include gain, filter cutoff frequency, and even ADC resolution and conversion time, as well as the obvious digital/MUX functions of input channel selection, output data format, and unipolar/bipolar range. The AD7890 is an example of a highly integrated monolithic data acquisition system. It has 8 multiplexed input channels, a SHA, an internal voltage reference, and a fast 12-bit ADC. Input scaling allows up to ±10V inputs when operating on a single +5V supply. Its block diagram is shown in Figure 6.12, and key specifications are summarized in Figure 6.13. Both AC and DC parameters are fully specified, simplifying the preparation of an error budget, and three types are available with three different standard input ranges:- AD7890-10 ±10 V AD7890-5 0 to 5V AD7890-2 0 to +2.5V AD7890 8-CHANNEL, 12-BIT, 100kSPS COMPLETE DATA ACQUISITION SYSTEM Figure 6.12
AD7890 SPECIFICATIONS ADC Conversion time 5.us SHA Acquisition Time 117kSPS Throughput Rate (Includes 0.6us Overhead) AC and DC Specifications Single +5V Operation Low Power drain: 30mw Power down mode 1mw Standard Input Ranges AD7890-10: 10v AD7890-5: 0 to +5V AD7890-2: 0to+2.5V 6.13 The input channel selection is via a serial input port a total of 5 bits of data control the AD7890 via a serial port 3 address bits select the input channel, a CoNV bit starts the A-D conversion, and 1 in the STBY register places the device in a power-down mode where its power consumption is under lmw. All timing takes place on the chip and a single external capacitor controls the acquisition time of the internal track-and-hold. A-D conversion may also be initiated externally using the CONVST pin. With the serial clock rate at its maximum of 10MHz, the achievable throughput rate for the AD7890 is 5.9us(conversion time)plus 0.6us(six serial clocks of internal overhead) plus 2us(acquisition time). This results in a minimum throughput time of 8. 5us(equivalent to a throughput rate of 117kSPS) The AD7890 draws 30mw from a +5V supply The entire family of AD789X 12-bit data acquisition ADCs is shown in Figure 6.14 The AD7890 and AD7891 are complete 8-channel data acquisition systems, while the AD7892, AD7893, and ad7896 are designed for use on a single channel, or with an external multiplexer
1 2 AD7890 SPECIFICATIONS ADC Conversion Time: 5.9 s SHA Acquisition Time: 2 s 117kSPS Throughput Rate (Includes 0.6 s Overhead) AC and DC Specifications Single +5V Operation Low Power Drain: Operational: 30mW Power Down Mode 1mW Standard Input Ranges AD7890 - 10: 10V AD7890 - 5: 0 to +5V AD7890 - 2: 0 to +2.5V Figure 6.13 The input channel selection is via a serial input port. A total of 5 bits of data control the AD7890 via a serial port:- 3 address bits select the input channel, a CONV bit starts the A-D conversion, and 1 in the STBY register places the device in a power-down mode where its power consumption is under 1mW. All timing takes place on the chip and a single external capacitor controls the acquisition time of the internal track-and-hold. A-D conversion may also be initiated externally using the CONVST pin. With the serial clock rate at its maximum of 10MHz, the achievable throughput rate for the AD7890 is 5.9µs (conversion time) plus 0.6µs (six serial clocks of internal overhead) plus 2µs (acquisition time). This results in a minimum throughput time of 8.5µs (equivalent to a throughput rate of 117kSPS). The AD7890 draws 30mW from a +5V supply. The entire family of AD789X 12-bit data acquisition ADCs is shown in Figure 6.14. The AD7890 and AD7891 are complete 8-channel data acquisition systems, while the AD7892, AD7893, and AD7896 are designed for use on a single channel, or with an external multiplexer
AD789X SERIES OF 12-BIT ADCs FOR DATA ACQUISITION ODEL AD7890AD7891 D7896 TPut(KSPS) 100 500/600 PwrSupplysv 2. 7 to Power 50mw Omw 45mW15mW@33 Interface Serial Paralle!Par/Ser Seria Pin Count Figure 6.14 The AD785X 12-bit low power data acquisition ADCs have been designed and fully specified for either +3v or +5V operation. This family includes parallel and serial single and 8-channel versions. The devices have self or system calibration modes for offset, gain, and the internal SAr dao AD785X SERIES OF 3V/5V 12-BIT ADCs MODEL AD7853 AD7854 AD7858 AD7859 AD7853u(AD7854)(AD7858L(AD7859u TPut(kSPS 200 (100) (100) Pwr Supply +3V, +5v+3V,+5v+3V,+5v+3V,+5v 15mw 15mw 15mw 15mw +3V 5.5mw) (5.5mw) 55mw(5.5mw Power Down Yes nterface Serial Parallel Pin Count 40/44 )VALUES FOR LOW POWER, L, VERSIONS Figure 6.15 MULTIPLEXING INPUTS TO SIGMA-DELTA ADCS was discussed in Section 3, the digital filter is an integral part of a sigma-delta ADC. When the input to a sigma-delta AdC changes by a large step the entire digital filter must fill with the new data before the output becomes valid, which slow process. This is why sigma-delta ADCs are sometimes said to be unsuitable multi-channel multiplexed systems- they are not inherently so, but the time taken to change channels can be inconvenient Figure 6.Ie ple, the AD7710-family of ADCs contains an on-chip multiplexer(see 16), and the digital filter(frequency response shown in Figure 6.17)
1 3 AD789X SERIES OF 12-BIT ADCs FOR DATA ACQUISITION Figure 6.14 The AD785X 12-bit low power data acquisition ADCs have been designed and fully specified for either +3V or +5V operation. This family includes parallel and serial single and 8-channel versions. The devices have self or system calibration modes for offset, gain, and the internal SAR DAC. AD785X SERIES OF 3V / 5V 12-BIT ADCs Figure 6.15 MULTIPLEXING INPUTS TO SIGMA-DELTA ADCS As was discussed in Section 3, the digital filter is an integral part of a sigma-delta ADC. When the input to a sigma-delta ADC changes by a large step, the entire digital filter must fill with the new data before the output becomes valid, which is a slow process. This is why sigma-delta ADCs are sometimes said to be unsuitable for multi-channel multiplexed systems - they are not inherently so, but the time taken to change channels can be inconvenient. As an example, the AD7710-family of ADCs contains an on-chip multiplexer (see Figure 6.16), and the digital filter (frequency response shown in Figure 6.17)