![](http://datasheet.mmic.net.cn/340000/AND8054_datasheet_16461858/AND8054_4.png)
AND8054/D
http://onsemi.com
4
Table 1. Summary of Capacitive Sensors
áááááááááááááááááááááááááááááá
á
á
á
áááááááááááááááááááááááááááááá
á
á
á
ááááááááááááááááááááááááááááááá
á
áááááááááááááááááááááááá
Sensor Configuration
áááááááááááááááááááááááááááááá
ááááááá
ááááááá
ááááááá
ááááááá
ááááááá
ááááááá
á
á
á
á
Absolute
CMEAS
Dual
á
á
áááááááá
á
á
áááááááá
áááááááá
Differential
á
áááááááá
áááááááá
áááááááá
Schematic Representation
áááááááá
áááááááá
áááááááá
Acceleration
Oil Level
CMEAS
áááááááá
áááááááá
áááááááá
áááááááá
áááááááá
áááááááá
freq.
á
áááááá
CREF
áááááá
áááááá
áááááá
á
á
á
á
á
Absolute Pressure
á
á
á
á
Displacement
Proximity
áááááááááááááááááááááááááááááá
ááááááá
á
áááááááá
áááááááá
á
áááááá
á
OSCILLATOR THEORY
An oscillator is a positive feedback control system which
does not have an external input signal, but will generate an
output signal if certain conditions are met. In practice, a small
input is applied to the feedback system from factors such as
noise pick–up or power supply transients, and this initiates the
feedback process to produce a sustained oscillation. A block
diagram of an oscillator is shown in Figure 3.
The poles of the denominator of the transfer equation T(s),
or equivalently the zeroes of the characteristic equation,
determine the time domain behavior of the system. If T(s)
has all of its poles located within the left plane, the system
is stable because the corresponding terms are all
exponentially decaying. In contrast, if T(s) has one pole that
lies within the right half plane, the system is unstable
because the corresponding term exponentially increases in
amplitude. An oscillator is on the borderline between a
stable and an unstable system and is formed when a pair of
poles is on the imaginary axis, as shown in Figure 4.
If the magnitude of the loop gain is greater than one and
the phase is zero, the amplitude of oscillation will increase
exponentially until a factor in the system such as the supply
voltage restricts the growth. In contrast, if the magnitude of
the loop gain is less than one, the amplitude of oscillation
will exponentially decrease to zero.
A
≡
Amplifier Gain
≡
Feedback Factor
+
–
Figure 3. Block Diagram of an Oscillator
V
OUT
V
IN
T(s)
VOUT
VIN
A
1
A
A
1
LG
A
s
A
N(s)
D(s)
where
A
LG
loop gain
s
characteristic equation
If VIN
0, then T(s)
when
s
0
|LG|
1 (magnitude) and
LG
0 (phase).
At the oscillation condition of s = 0, referred
to as the Barkhausen stability
criterion,
Imaginary (j
ω
)
Imaginary (j
ω
)
Real (
ω
)
Real (
ω
)
2nd Order Oscillator
3rd Order Oscillator
Figure 4. Pole Locations for a 2nd and 3rd Order Oscillator