HD6432646 Hitachi, HD6432646 Datasheet - Page 642

• Manufacturer Part Number: HD6432646
• Description: (HD64F264x Series) 16-Bit Microcomputer
• Manufacturer: Hitachi

Permissible Signal Source Impedance: H8S/2646 Series analog input is designed so that
conversion precision is guaranteed for an input signal for which the signal source impedance is 10
k or less. This specification is provided to enable the A/D converterÕs sample-and-hold circuit
input capacitance to be charged within the sampling time; if the sensor output impedance exceeds
10 k, charging may be insufficient and it may not be possible to guarantee the A/D conversion
precision.
However, if a large capacitance is provided externally, the input load will essentially comprise
only the internal input resistance of 10 k, and the signal source impedance is ignored.
However, since a low-pass filter effect is obtained in this case, it may not be possible to follow an
analog signal with a large differential coefficient (e.g., 5 mV/µs or greater).
When converting a high-speed analog signal, a low-impedance buffer should be inserted.
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Figure 16-10 A/D Conversion Precision Definitions (2)
Digital output
Ideal A/D conversion
characteristic
Offset error
Actual A/D conversion
characteristic
Nonlinearity
error
Full-scale error
Analog
input voltage
FS