Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
1999-02-26
2001-03-20
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S309000, C327S313000, C327S314000, C327S374000, C327S375000, C361S056000
Reexamination Certificate
active
06204715
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to signal amplifying circuitry and more specifically to such circuitry for amplifying signals provided by piezoelectric sensors.
BACKGROUND OF THE INVENTION
Electronic amplifiers for amplifying signals generated by analog sensors and/or transducers are known and have been extensively used in the automotive industry for decades. One particular class of transducers with which such amplifiers are often implemented are known as piezoelectric sensors, examples of which include pressure sensors, accelerometers and the like. Piezoelectric sensors are “self-generating” transducers in that they do not require externally supplied electrical power to generate output signals under dynamic mechanical loading conditions.
When dynamically loaded, piezoelectric sensors produce a high-impedance differential charge signal. In some applications, the ground-isolated differential output signal is amplified via a two-input signal amplifier, and in other applications one end of the differential charge signal is grounded (typically to the sensor housing) and a single-ended output is amplified via a single-input amplifier. In either case, electronic amplifiers for use with such piezoelectric sensors are operable to convert the high-impedance charge signal to a low-impedance voltage usable by signal processing circuitry such as a so-called engine control module (ECM), powertrain control module (PCM) or the like.
Generally, four basic amplifier configurations are used in the automotive and related industries for amplifying piezoelectric sensor signals:
a voltage amplifier using an operational amplifier, a charge amplifier using an operational amplifier, a current integrator using a number of operational amplifiers, and a unity-gain source follower amplifier using a field effect transistor. While each of the foregoing amplifier configurations are generally capable of appropriately conditioning the sensor output signals under some operating conditions, known embodiments of these amplifier configurations have certain drawbacks associated therewith and are accordingly incapable of satisfying demanding underhood requirements while maintaining desired operational characteristics as well as acceptable manufacturing goals (i.e., cost and ease of fabrication).
For example, one prior art sensor amplifying circuit
10
of the voltage amplifier type is illustrated in FIG.
1
. Circuit
10
includes a piezoelectric sensor
12
having a single-ended input connected to an input VIN of a signal amplifier circuit
14
. VIN is connected to a non-inverting input of a known operational amplifier
16
, to one end of a capacitor C and to one end of a resistor R
2
, the opposite ends of which are connected to a REF output of circuit
14
. The REF output is typically connected to ground potential in operation. The inverting input of amplifier
16
is connected to one end of another resistor R
1
and to one end of a feedback resistor RF. The opposite end of R
1
is connected to REF, and the opposite end of RF is connected to an output of amplifier
16
which provides the amplified sensor signal VOUT. Amplifier
16
requires connections to REF and to a power supply VCC for operation. While amplifier circuit
14
provides for satisfactory signal conditioning operation, operational amplifiers rated for underhood applications (i.e., −40° C. to +150° C.) are generally cost prohibitive.
An example of another prior art sensor amplifying circuit
20
of the charge amplifier type is illustrated in FIG.
2
. Circuit
20
includes a piezoelectric sensor
12
having a sensor output connected to an input VIN of a signal amplifying circuit
22
. VIN is connected to one end of a resistor R
1
, the opposite end of which is connected to an inverting input of an operational amplifier
24
. The inverting input of amplifier
24
is also connected to one end of a feedback resistor RF and to one end of a capacitor C, the opposite ends of which are connected to an output of amplifier
24
which provides the amplified sensor signal VOUT. The non-inverting input of amplifier
24
is connected to one end of a resistor RA and to one end of another resistor RB. The opposite end of RA is connected to a power supply input VCC and the opposite end of RB is connected to a REF input which is typically connected to ground potential. The operational amplifier
24
must also be connected to VCC and REF for operation thereof.
Charge amplifiers of the type illustrated in
FIG. 2
are widely used for amplifying signals produced by piezoelectric sensors and are commonly used in instrumentation applications employing pressure, force and/or acceleration sensors. The output voltage VOUT of amplifier circuit
22
is negatively proportional to the input charge and is determined solely by the feedback capacitor C. With the non-inverting input set at a DC reference voltage VREF, and the inverting input comprising a virtual ground node, the operational amplifier
24
drives the output in such a manner that the input voltages are equal. RF and C comprise a high-pass filter and determine the low frequency characteristics of the amplifier.
The amplifier circuit
22
has several practical drawbacks associated therewith. For example, as with amplifier circuit
14
of
FIG. 1
, an operational amplifier
24
rated for underhood applications is typically cost prohibitive. Moreover, circuit
22
has a long power-up delay (up to 10 seconds) due to the large component values often required for RF and C. The circuit configuration illustrated in
FIG. 2
can be enhanced to address the foregoing deficiencies but doing so undesirably adds further cost to sensor circuit
20
.
An example of another prior art sensor amplifying circuit
30
of the current integrator type is illustrated in FIG.
3
. Circuit
30
includes a piezoelectric sensor
12
having a sensor output connected to an input VIN of a signal amplifying circuit
32
. VIN is connected to an inverting input of a first operational amplifier circuit
34
and to one end of a first feedback resistor RF
1
. The opposite end of RF
1
is connected to an output V
1
of amplifier
34
and to one end of a capacitor C
1
. The opposite end of C
1
is connected to one end of a resistor R
1
, the opposite end of which is connected to an inverting input of a second operational amplifier
36
, one end of a second feedback resistor RF
2
and one end of a capacitor C
2
. The opposite ends of RF
2
and C
2
are connected to an output of amplifier
36
which provides the amplified sensor signal VOUT. The non-inverting inputs of amplifiers
34
and
36
are connected to a REF input which is typically connected to ground potential. As with the amplifier circuits of
FIGS. 1 and 2
, amplifiers
34
and
36
include connections to an external power supply VCC and to REF.
Amplifier
34
comprises a current to voltage converter which provides an output proportional to the change in sensor output. C
1
blocks the DC component of V
1
and amplifier
36
comprises a conventional voltage integrator and integrates the AC component of V
1
to produce a signal proportional to the mechanical force acting on sensor
12
. As with the amplifier circuits of
FIGS. 1 and 2
, the cost of operational amplifiers
34
and
36
, if rated for underhood applications, is cost prohibitive. Moreover, the size and cost of capacitor C
1
is excessive and accordingly impractical for use integral with the sensor
12
.
An example of another prior art sensor amplifying circuit
40
of the unity-gain source follower FET type is illustrated in FIG.
4
. Circuit
40
includes a piezoelectric sensor
12
having a sensor output connected to an input VIN of a signal amplifying circuit
42
. VIN is connected to a gate of a p-channel enhancement mode metal oxide semiconductor field effect transistor (MOSFET) M
1
, to one end of a resistor R
3
and to one end of a capacitor CR. The opposite end of R
3
is connected to one end of a resistor R
1
and to one end of a resistor R
2
. The opposite end of R
1
is connected to the sou
Sellnau Mark C.
Tidrow Raymond A.
Callahan Timothy P.
General Motors Corporation
Grove George A.
Luu An T.
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