HD6413007F20 Datasheet, PDF (563/798 Pages) Renesas Technology Corp – Hardware Manual Renesas 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Series

Digital
output
Ideal A/D
conversion
characteristic
Full-scale
error
15. A/D Converter
Nonlinearity
error
Actual A/D conversion
characteristic
Offset error
FS
Analog input
voltage
Figure 15.10 A/D Converter Accuracy Definitions (2)
7. Allowable Signal-Source Impedance: The analog inputs of the H8/3006 and H8/3007 are
designed to assure accurate conversion of input signals with a signal-source impedance not
exceeding 10 kΩ. The reason for this rating is that it enables the input capacitor in the sample-
and-hold circuit in the A/D converter to charge within the sampling time. If the sensor output
impedance exceeds 10 kΩ, charging may be inadequate and the accuracy of A/D conversion
cannot be guaranteed.
If a large external capacitor is provided in single mode, then the internal 10-kΩ input
resistance becomes the only significant load on the input. In this case the impedance of the
signal source is not a problem.
A large external capacitor, however, acts as a low-pass filter. This may make it impossible to
track analog signals with high dv/dt (e.g. a variation of 5 mV/μs) (figure 15.11). To convert
high-speed analog signals or to use scan mode, insert a low-impedance buffer.
Rev.5.00 Sep. 12, 2007 Page 533 of 764
REJ09B0396-0500