JPS5938729Y2 - CR oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a CR oscillator that can improve variable frequency characteristics and reduce costs.

For example, CR oscillators such as phase-shifting oscillators, Winbridge oscillators, and Salzer oscillators use frequency determining elements consisting of capacitors and resistors in their frequency determining circuits.

In addition, as this frequency determining element, a variable range is set by switching multiple resistors with a changeover switch, and a variable air capacitor is used to continuously change the range within that range due to requirements such as linearity, stability, and durability. FIG. 1 is a block diagram showing an example of this type of CR oscillator. In the figure, 1 is a frequency determining circuit, and 2 is an amplifier for amplifying the oscillation output of the frequency determining circuit 1.

3 is a feedback resistor inserted between the output of the amplifier 2 and the differential input, and 4 is an amplitude control circuit.

Reference numeral 5 denotes a shield box or enclosure provided to electrostatically and magnetically shield the frequency determining circuit 1 from disturbances from other signal sources. I am trying to connect it to the electric potential.

Furthermore, in order to make the overall shape smaller, the shape of the outer enclosure 5 must also be made smaller.

However, the variable air capacitor, so-called variable capacitor, used as an element of the frequency determining circuit has a larger shape than other circuit components, and therefore a large stray capacitance occurs between these elements and the outer enclosure 5. When is small, the two become close and the stray capacitance also increases.

For this reason, the oscillation frequency deviates from the theoretical value, causing problems with the linearity and stability of frequency changes, and this stray capacitance must be corrected.

Furthermore, if a small variable air capacitor is used to downsize the circuit, the above-mentioned stray capacitance may be larger than the capacitance of the variable air capacitor.

In this case, the above-mentioned stray capacitance correction is severely limited by the linearity of frequency change.

Furthermore, since the variable capacitor used as an element of the frequency determining circuit is mechanically rotated, the stray capacitance varies depending on the rotation angle and is not constant, so it is extremely difficult to accurately compensate for this. Ta.

Furthermore, since the outer enclosure 5 is connected to the ground potential, insulation resistance between the frequency determining circuit 1 and the outer enclosure 5 poses a problem.

That is, when a resistor with a large resistance value is used as the resistor of the frequency determining element, it is necessary to use a material with high insulation resistance and excellent dielectric constant as a mounting material, which causes a problem of increased cost.

The present invention was developed in view of the above circumstances, and even if there is stray capacitance between the elements of the frequency determining circuit and the surrounding area, it is possible to ignore this and set the oscillation conditions, thereby improving the frequency variable characteristics. It is an object of the present invention to provide a CR oscillator which is of good quality and whose outer dimensions can be reduced to the necessary minimum, which allows the use of a small-sized variable capacitor, thereby providing a wide frequency variable range.

An embodiment of the present invention will be described below with reference to the block diagram shown in FIG.

Note that the same parts as in FIG. 1 are given the same reference numerals and their explanations will be omitted.

In the figure, reference numeral 6 denotes an amplifier to which the output of the frequency determining circuit 1 is applied, and the output of this amplifier 6 is connected to the outer enclosure 5.

Note that this amplifier 6 is a non-inverting amplifier whose input/output characteristics are in phase, and the amplification degree is always set to 1.

Therefore, the envelope 5 is driven by the output of the amplifier 6 in phase with the output of the frequency determining circuit 1, and their potentials become equal.

Therefore, no current flows between the output side of the frequency determining circuit 1 and the elements of the frequency determining circuit placed at the same potential as the output side and the enclosure 5.

On the other hand, the charge Q stored in the capacitor is given by Q=CV, and in this case, there is no potential difference between the envelope 5 and the part having the same potential as the output side of the element of the frequency determining circuit, so no charge is stored at all.

Therefore, the stray capacitance between the part having the same potential as the output side of the element and the outer enclosure 5 can be ignored.
The influence of can be removed.

For this reason, there is no need to correct stray capacitance occurring between the frequency determining circuit 1 and its envelope 5, and the oscillation conditions are not impaired in any way, so an ideal state can be achieved.

On the other hand, even if disturbances from other signal sources are induced into the surrounding area,
Since the amplifier 6 is inserted from the output side to the outer enclosure to the extent that it disturbs the potential, the output cartwheel and frequency determining circuit is not affected by disturbance at all, and the burden on the amplitude control circuit 4 can be reduced. It is possible to improve the amplitude stability when variable, and to lower the distortion rate of the oscillation wave.

- Also, since the presence of the stray capacitance can be ignored, a wide variable frequency range can be obtained by using a variable capacitor with a small capacitance, and the overall size can be reduced.

Furthermore, since no current flows between the frequency determining circuit 1 and its envelope 5, the equivalent admittance becomes zero, and the apparent insulation resistance becomes infinite.

Therefore, it is not necessary to use a material with exceptionally high insulation resistance and exceptionally excellent dielectric constant as a mounting material for the frequency determining element, and costs can be reduced.

FIG. 3 is a block diagram of another embodiment of the present invention, in which the same parts as in FIG. be.

Further, the outer enclosure 5 that shields the frequency determining circuit 1 is not limited to surrounding the entire circuit, but may surround a specific main part.

As described in detail above, the present invention provides an output signal via an amplifier to a shield box housing a frequency determining circuit therein, and maintains the output signal at the same phase and potential.

Therefore, it is possible to provide an inexpensive CR oscillator with good frequency variable characteristics and oscillation characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional CR oscillator, FIG. 2 is a block diagram showing one embodiment of the present invention, and FIG. 3 is a block diagram showing another embodiment of the present invention. 1... Frequency determination circuit, 5... Shield box (outer enclosure)
.

Claims (1)

[Scope of utility model registration request] A shield box that performs electrostatic adduction and magnetic shielding,
A CR oscillator comprising a frequency determining circuit that is housed in the shield box and determines the frequency of the oscillation output, and an amplifier that amplifies the output of the frequency determining circuit in phase and applies it to the shield box.