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ADS1210 Datasheet(PDF) 12 Page - Texas Instruments |
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ADS1210 Datasheet(HTML) 12 Page - Texas Instruments |
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12 / 50 page  ADS1210, ADS1211 12 SBAS034B www.ti.com Filter Equation The digital filter is described by the following transfer function: where N is the Decimation Ratio. This filter has a (sin(x)/x)3 response and is referred to a sinc3 filter. For the ADS1210/11, this type of filter allows the data rate to be changed over a very wide range (nearly four orders of magnitude). However, the –3dB point of the filter is 0.262 times the data rate. And, as can be seen in Figures 1 and 2, the rejection in the stopband (frequencies higher than the first notch frequency) may only be –40dB. These factors must be considered in the overall system design. For example, with a 50Hz data rate, a significant signal at 75Hz may alias back into the passband at 25Hz. The analog front end can be designed to provide the needed attenuation to prevent aliasing, or the system may simply provide this inherently. Another possibility is increasing the data rate and then post filtering with a digital filter on the main controller. Filter Settling The number of modulator results used to compute each conversion result is three times the Decimation Ratio. This means that any step change (or any channel change for the ADS1211) will require at least three conversions to fully settle. However, if the change occurs asynchronously, then at least four conversions are required to ensure complete set- tling. For example, on the ADS1211, the fourth conversion result after a channel change will be valid (see Figure 4). |H (f ) | = sin π• f • N f MOD N • sin π• f f MOD 3 the effective resolution of the output data at a given data rate, but there is also an increase in power dissipation. For Turbo Mode Rates 2 and 4, the increase is slight. For rates 8 and 16, the increase is more substantial. See the Typical Perfor- mance Curves for more information. In a Turbo Mode Rate of 16, the ADS1210/11 can offer 20 bits of effective resolution at a 1kHz data rate. A comparison of effective resolution versus Turbo Mode Rates and output data rates is shown in Table IV while Table V shows the corresponding noise level in µVrms. TURBO MODE The ADS1210/11 offers a unique Turbo Mode feature which can be used to increase the modulator sampling rate by 2, 4, 8, or 16 times normal. With the increase of modulator sampling frequency, there can be a substantial increase in DATA TURBO TURBO TURBO TURBO TURBO RATE MODE MODE MODE MODE MODE (HZ) RATE 1 RATE 2 RATE 4 RATE 8 RATE 16 10 21.5 22.0 22.5 20 21.0 22.0 22.0 22.5 40 20.0 21.5 22.0 22.5 23.0 50 20.0 21.5 21.5 22.0 23.0 60 19.5 21.0 21.5 22.0 23.0 100 18.0 20.0 21.0 21.5 22.5 1000 10.0 12.5 15.0 17.5 20.0 EFFECTIVE RESOLUTION (BITS RMS) TABLE IV. Effective Resolution vs Data Rate and Turbo Mode Rate. (Gain setting of 1 and 10MHz clock.) DATA TURBO TURBO TURBO TURBO TURBO RATE MODE MODE MODE MODE MODE (Hz) RATE 1 RATE 2 RATE 4 RATE 8 RATE 16 10 2.9 1.7 1.3 20 4.3 2.1 1.7 1.3 40 6.9 3.0 2.3 1.6 1.0 50 8.1 3.2 2.4 1.8 1.0 60 10.5 3.9 2.6 1.9 1.0 100 26.9 6.9 3.5 2.7 1.4 1000 6909.7 1354.5 238.4 46.6 7.8 TABLE V. Noise Level vs Data Rate and Turbo Mode Rate. (Gain setting of 1 and 10MHz clock.) NOISE LEVEL ( µVrms) The Turbo Mode feature allows trade-offs to be made between the ADS1210/11 XIN clock frequency, power dissi- pation, and effective resolution. If a 5MHz clock is available but a 10MHz clock is needed to achieve the desired perfor- mance, a Turbo Mode Rate of 2X will result in the same effective resolution. Table VI provides a comparison of effective resolution at various clock frequencies, data rates, and Turbo Mode Rates. DATA XIN CLOCK TURBO EFFECTIVE RATE FREQUENCY MODE RESOLUTION (Hz) (MHz) RATE (Bits rms) 60 10 1 19.5 60 5 2 19.5 60 2.5 4 19.5 60 1.25 8 19.5 60 0.625 16 19.5 100 10 1 18.0 100 5 2 18.0 100 2.5 4 18.0 100 1.25 8 18.0 100 0.625 16 18.0 TABLE VI. Effective Resolution vs Data Rate, Clock Frequency, and Turbo Mode Rate. (Gain set- ting of 1.) FIGURE 4. Asynchronous ADS1210/11 Analog Input Volt- age Step or ADS1211 Channel Change to Fully Settled Output Data. DRDY Serial I/O Valid Data Valid Data Valid Data Valid Data Data not Valid Data not Valid Data not Valid Significant Analog Input Change or ADS1211 Channel Change t DATA |
Número de pieza similar - ADS1210_15 |
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Descripción similar - ADS1210_15 |
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