Epson S1C63656 Technical Manual page 120

CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (R/f Converter)
The CR oscillation circuit is designed so that either the reference resistance side or the sensor side can
be operated independently by the oscillation control circuit.
Each circuit performs the same oscillating operation as follows:
The Tr1 (Tr2) turns on first, and the capacitor connected between the REF (SEN) and V
charged through the reference resistance (sensor). If the voltage level of the RFIN terminal decreases,
the Tr1 (Tr2) turns off and the Tr3 turns on. As a result, the capacitor becomes discharged, and oscilla-
tion is performed according to CR time constant. The time constant changes as the sensor resistance
value fluctuates, producing a difference from the oscillation frequency of the reference resistance.
Oscillation waveforms are shaped by the schmitt trigger and transmitted to the measurement counter.
The clock transmitted to the measurement counter is also output from the RFOUT terminal while the
sensor is oscillating. As a result, oscillation frequency can be identified by the oscilloscope. Since this
monitor has no effect on oscillation frequency, it can be used to adjust R/f conversion accuracy.
Oscillation waveforms and waveforms output from the RFOUT terminal are shown in Figure 4.14.2.3.
The "L" pulse width of the RFOUT output must be 10 µsec or more (when V
kΩ, C = 1000 pF).
RF
110
Oscillation
control
circuit
Count
clock
Fig. 4.14.2.2 CR oscillation circuit (DC bias)
RFIN0/1 terminal
RFOUT output
Fig. 4.14.2.3 Oscillation waveform
V
DD
Tr2
SEN0(1)
Tr1
REF0(1)
RFIN0(1)
Tr3
V
SS
RFOUT
10 µsec or more
EPSON
V
SS
terminals is
SS
= 3.0 V, R
DD SEN0/1
V
DD
V
SS
V
DD
V
SS
S1C63656 TECHNICAL MANUAL
= 50