H8SLASH3021 datasheet(463/712 Pages) RENESAS

463 / 712 page

13. A/D Converter

Rev.2.00 Mar. 22, 2007 Page 439 of 684

REJ09B0352-0200

Offset error

Nonlinearity

error

Actual A/D conversion

characteristic

Analog

input voltage

Digital output

Ideal A/D conversion

characteristic

Full-scale error

Figure 13.10 A/D Conversion Precision Definitions (2)

Permissible Signal Source Impedance: H8/3022 Group analog input is designed so that

conversion precision is guaranteed for an input signal for which the signal source impedance is 5

Ω or less. This specification is provided to enable the A/D converter’s sample-and-hold circuit

input capacitance to be charged within the sampling time; if the sensor output impedance exceeds

5 k

Ω, charging may be insufficient and it may not be possible to guarantee the A/D conversion

precision.

When converting in the single mode, if a large capacitance is provided externally, the input load

will essentially comprise only the internal input resistance of 10 k

Ω, 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., voltage regulation 5 mV/

μs or greater).

(See figure 13.11.)

When converting a high-speed analog signal and when performing conversion in the scan mode, a

low-impedance buffer should be inserted.

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