Data Sheet

Q4000 Technical Data Sheet
Document 1135-0902, REV K 18
4 Customer Input/Output Interfaces
External Interfaces 4.1
Analog Inputs 4.1.1
Two available: Pins 29 and 31:
• 0 – 3.5 Volts.
• 12 bit resolution
• Greater than1MΩ input impedance
• 3dB bandwidth and 160 kHz if driven with low impedance. The “greater than 1 M Ω” is at DC only. If
you try to sample a frequency (not DC) of 160KHz at the input, it will be down in amplitude by half
power at the internal ADC input. If you go higher in frequency, the amplitude will be reduced more.
This would give a false amplitude reading. This translates to a maximum sample rate of 7 to 8
microseconds.
There is a capacitor on the input of the Q4000 for the ADCs. If you place a series resistance in the
line with the ADC input, the reduction mentioned above is made worse. If you make that resistance 0
ohms the spec remains at 160KHz.
Figure 4-1, Analog Input Circuit
4.1.1.1 Sample Circuits for Appropriate Scaling to 0-3.5V
Analog inputs are 12 bits and have a Full Scale (F
scale
) reading of 4095. The equation below can be used to
determine the resistor values for varying maximum sensor voltage readings.
( )
2
21
5.3
R
RR
VoltageScaleFullV
s
F
+
=
=
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