W925E240 Datasheet, PDF (54/73 Pages) Winbond – 8-BIT CID MICROCONTROLLER

W925E/C240
Input Pre-Processor
The input signal is processed by Input Pre-Processor, which is comprised of two OP amps and a bias
source(VREF). The gain OP-amps are used to bias the input voltage with the VREF signal voltage.
VREF is V_AD/2 typically, this pin is recommended to connect a 0.1uF capacitor to V_AS. The gain
adjustable OP amps are sued to select the input gain by connecting a feedback resistor between
GCFB and INN pins. Figure 6-16 shows the differential input configuration and Figure 6-17 shows the
single-ended configuration.
VREF
0.1uF
R3 R4
C1
R1
INP
+
C2
R2
INN -
R5 GCFB
Differential Input Amplifier
C1 = C2
R1 = R2
R3 = (R4 R5) / (R4 + R5)
Voltage Gain
Av = R5 / R1
Input Impedance
Zin = 2 R1² + (1 / wC)²
Figure 6-16 Differential Input Gain Control Circuit
0.1uF
VREF
C
R1
22n
INP
+
INN -
R2 GCFB
Voltage Gain
Av = R2 / R1
Figure 6-17 Single-Ended Input Gain Control Circuit
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