HD6412340 HITACHI [Hitachi Semiconductor], HD6412340 Datasheet - Page 536

• Manufacturer Part Number: HD6412340
• Description: H8S/2345 F-ZTAT Hardware Manual
• Manufacturer: HITACHI [Hitachi Semiconductor]

Permissible Signal Source Impedance: H8S/2345 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 converter's 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/ s or greater).
When converting a high-speed analog signal, a low-impedance buffer should be inserted.
Figure 14.10 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
523