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A-3 Analog Input [T-Series Datasheet]

General Info

Table A.3-1. T7 Analog Input Information.  All specs at room temperature unless otherwise noted.

  Conditions Min Typical Max Units
           
Typical Input Range [1] Gain=1 -10.5   10.1 Volts
Max AIN Voltage to GND [2] Valid Readings -11.5   11.5 Volts
Max AIN Voltage to GND [3] No Damage -20   20 Volts
Input Bias Current [4]     20   nA
Input Impedance [4]     1  
Max Source Impedance [4]     1  
           
Integral Linearity Error Range=10, 1, 0.1     ±0.01 %FS
  Range=0.01     ±0.1 %FS
           
Absolute Accuracy Range=10, 1, 0.1     ±0.01 %FS
  Range=10     ±2000 μV
  Range=1     ±200 μV
  Range=0.1     ±20 μV
  Range=0.01     ±0.1 %FS
  Range=0.01     ±20 μV
           
Temperature Coefficient     15   ppm/°C
           
Channel Crosstalk [5] < 1kHz   -100   dB
  1kHz - 50kHz   20   dB/dec
           
High-Speed ADC -3dB Frequency [6] Gain=1, 10   445   kHz
  Gain=100   337   kHz
  Gain=1000   63   kHz
           
High-Res ADC -3dB Frequency [7] See Note #7        
           
Noise (Peak-To-Peak) See A-3-1     <1 μV
Effective Resolution (RMS) See A-3-1     22 bits
Noise-Free Resolution See A-3-1     20 bits
           
[1] Differential or single-ended     
[2] This is the maximum voltage on any AIN pin compared to ground for valid measurements on that channel. For single-ended readings on the channel itself, inputs are limited by the "Typical Input Range" above, and for differential readings consult Appendix A-3-2 Signal Range. Further, if a channel has over 13.0 volts compared to ground, readings on other channels could be affected. Because all even channels are on one front-end mux and all odd channels on a second front-end mux, an overvoltage (>13V) on a single channel will generally affect only even or only odd channels.     
[3] Maximum voltage, compared to ground, to avoid damage to the device. Protection level is the same whether the device is powered or not.     
[4] The key specification here is the maximum source impedance. As long as your source impedance is not over this value, there will be no substantial errors due to impedance problems. For source impedance greater than this value, more settling time might be needed.     
[5] Typical crosstalk on a grounded AIN pin, with 20Vpp sine wave on adjacent AIN pin. An adjacent AIN pin refers to multiplexer channel location not channel number, e.g. AIN0-AIN2 or AIN1-AIN3 pairs.     
[6] This is the bandwidth of the analog hardware.  Any frequencies less than this will go through the analog system to the ADC and be part of the digitized waveform.  For DC measurements this is of little concern as ResolutionIndex and averaging can be used to get rid of extra noise. For AC measurements, frequency components below the nyquist point can be removed after digitizing, but frequency components above the nyquist point must be removed before digitizing as they will alias.  If unwanted signals with frequencies between the nyquist point and analog cutoff frequency are expected, and they are expected to have sufficient magnitude to be above the acceptable noise level, then an external hardware filter must be used (often called an anti-alias or anti-aliasing filter).
[7] The fixed -3dB frequencies from note 6 apply to the high-speed ADC (ResolutionIndex = 1-8), but the high-resolution ADC on the T7-Pro (ResolutionIndex = 9-12) has filtering at much lower frequencies.  The frequency response at ResolutionIndex=12 is shown in Figure 22 of the AD7190 datasheet.  For the response at ResIndex 9/10/11 multiply those x-axis values by 47.9/12.0/2.4.  Figure 22 only shows up to 150 Hz, but know that all higher frequencies are also filtered out, except for a narrow passband at 307 kHz.  The width of this passband is about 200 Hz at ResIndex=12 increasing to about 10000 Hz at ResIndex=9.

See also: Appendix A-3-1 Noise and Resolution