Oscillators – Automatic frequency stabilization using a phase or frequency... – With reference oscillator or source
Reexamination Certificate
2001-06-05
2002-11-26
Pascal, Robert (Department: 2817)
Oscillators
Automatic frequency stabilization using a phase or frequency...
With reference oscillator or source
C331S074000, C331S158000, C310S317000, C310S319000, C310S316010
Reexamination Certificate
active
06486743
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for driving and detecting an oscillator for use in, for example, an angle sensor, more specifically, to a device for driving and detecting an oscillator so as to stably drive and detect the oscillator by removing noise produced in the sensor.
2. Description of the Prior Art
FIG. 7
is a block diagram showing a conventional device for driving and detecting an oscillator as well as the construction of part of a angular speed sensor.
The angular speed sensor shown in
FIG. 7
has an oscillator
1
as sensing means, a drive control portion for oscillating and driving the oscillator
1
at a predetermined driving frequency, a detection control portion for detecting an angular speed outputted from the oscillator
1
, and a correction portion for making sensitivity adjustment and offset adjustment for the oscillator
1
varied by temperature.
The oscillator
1
is, for example, a piezoelectric type oscillator or a capacitance type oscillator, and has a plurality of oscillation legs (for example, three legs) formed in a branched manner at one of the ends of the oscillator
1
extending longitudinally. A pair of input electrodes extending longitudinally are formed in one of the faces of each of the oscillation legs, and a pair of output electrodes are likewise formed in the other face (not shown). In the oscillator
1
, when a sine-wave driving signal is given from a drive means
6
to the input electrodes of each of the oscillation legs, the oscillation legs are oscillated and driven in the direction in which the oscillation legs are aligned. In this state, when the oscillator
1
is placed on the longitudinal axis, Coriolis force produced corresponding to the magnitude of rotation allows the oscillator
1
to be deflected and deformed in the direction orthogonal to the oscillation direction. In this deformation, a pair of the output electrodes defined in the other face formed in the oscillator
1
output output signals of different phases corresponding to the magnitude of the Coriolis force.
The drive control portion is constructed of a PLL (phase-locked loop) consisting of binarization means
2
, a phase detection portion
3
, a VCO (voltage control oscillator)
4
, a frequency divider
5
, and the drive means
6
. When a driving signal SD is outputted from the drive means
6
and inputted to the oscillator
1
, output signals S
1
, S
2
are outputted from the oscillator
1
.
The phase detection portion is constructed of the phase difference detection portion
3
and a low-pass filter
7
, and outputs an angular speed output Sp corresponding to the magnitude of the Coriolis force based on the phase difference between the both output signals S
1
, S
2
outputted from the oscillator
1
. An oscillating signal generated by the VCO
4
is frequency-divided by the frequency divider
5
. The resulting signal is then sent out, as a reference signal Dref, to a sequence controller
9
at the correction side.
The correction portion is constructed of correction means
8
, the sequence controller
9
, an E
2
PROM
10
, an E
2
PROM interface
11
, a RAM (Random Access Memory)
12
, and a temperature sensor
13
. The correction means
8
has a correction circuit
8
A consisting of a sensitivity correction circuit, an offset correction circuit, and a temperature coefficient correction circuit, and amplification means
8
B.
The E2PROM
10
holds various initial data pieces for sensitivity adjustment, offset adjustment, and temperature coefficient of the oscillator
1
at a certain temperature (for example, 20° C.). In the correction means
8
, the respective initial data pieces held in the E
2
PROM at predetermined time intervals based on the reference signal Dref given from the frequency divider
5
under control of the sequence controller
9
are sent out through the E
2
PROM interface
11
to the RAM
12
. In other words, the contents of the RAM
12
is always overwritten with the initial data pieces having the same contents. When the contents of the initial data pieces recorded into the RAM
12
are changed even temporarily due to the influence of noise, the original initial data pieces can be returned immediately.
The correction circuit
8
A is provided in its interior with D/A conversion means, not shown, for converting each piece of the initial data pieces to an analog signal. The correction circuit
8
A is also fed temperature data piece detected by the temperature sensor
13
. The correction circuit
8
A selects a sensitivity correction value, a temperature correction value, and a temperature coefficient based on the temperature data piece detected by the temperature sensor
13
, and determines a proper amount of offset. The amount of offset is given to the amplification means
8
B so as to correct the angular speed output Sp outputted from the phase detection portion
3
. The corrected output, whose high-frequency component is removed by the low-pass filter, is outputted as a final angular speed output Sp′.
The conventional device for driving and detecting an oscillator has the following problems.
In the abovementioned construction, for example, the binarization process in the binarization means
2
is performed at a frequency in which the frequency of the oscillating signal of the VCO
4
is frequency-divided bisectionally five times (1/32 times), and writing from the E
2
PROM
10
to the RAM
12
is performed at a frequency in which the oscillating signal of the VCO
4
is frequency-divided bisectionally (1/2 times). In this case, the timing in which the output signals S
1
, S
2
of the oscillator
1
are binarized by the binarization means
2
, and the timing in which the respective initial data pieces in the E
2
PROM are written into the RAM
12
in the correction portion, correspond with each other once in every 16 times.
When the respective initial data pieces of the E
2
PROM
10
is written into the RAM
12
, noise tends to occur.
When the timings of both correspond with each other, a whisker noise is superimposed on the input signal of the binarization means
2
(an output signal of the oscillator
1
and/or a threshold value for binarizing the output signal). When the timings of both do not correspond with each other, the whisker noise is not superimposed on the input signal at all.
As described above, when the whisker noise is superimposed on the input signal, binary signals D
1
, D
2
are varied, and the phase difference between the both signals is also varied due to the variation. For this reason, the control voltage of the VCO
4
is fluctuated, so that the oscillating signal of the VCO
4
is also varied. This fact causes the signals of the entire driving and detecting device to be varied. Since this state is just similar to the state the driving signal SD for driving the oscillator
1
is FM-modulated, the oscillator
1
cannot be driven stably.
The binary signals D
1
, D
2
themselves are varied at a relatively high frequency, but the angular speed output Sp outputted from the phase difference detection portion
3
is varied at a low frequency. It is thus difficult to remove the variation in the low-pass filter
7
at the later stage. The angular speed output Sp′ with high accuracy cannot be detected.
SUMMARY OF THE INVENTION
The present invention solves the foregoing conventional problems, and an object of the present invention is to provide a device for driving and detecting an oscillator so as to be driven stably without being affected by noise.
Another object of the present invention is to provide a device for driving and detecting an oscillator so as to detect an angular speed with high accuracy without being affected by noise.
According to the present invention, a device for driving and detecting an oscillator comprises an oscillator for outputting output signals of different phases when an angular speed is given, a drive control portion for driving the oscillator, and a detection control portion for detecting the angular speed output based on the output signa
Hasegawa Kazuo
Takai Daisuke
Alps Electric Co. LTD
Beyer Weaver & Thomas LLP
Glenn Kimberly E
Pascal Robert
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