JPH02214313A - Frequency adjusting circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a frequency adjustment circuit for a crystal oscillation circuit for generating a timing clock for a logic circuit or the like.

2. Description of the Related Art Conventionally, a crystal oscillation circuit for generating a timing clock for a logic circuit, etc., generally has a circuit configuration shown in broken line 1 in FIG. 3. At the broken line part 1Vc in Figure 3, 2
is an inverter such as TTI or CMO8, 3 is a crystal oscillator,
4 is a feedback resistor that determines the bias potential of the inverter, and 6 and 6 are capacitors for stabilizing oscillation. With the above configuration, an oscillation circuit with a temporally stable frequency is obtained, but the initial frequency deviation of the crystal oscillator 3 (approximately ωPP
The initial frequency must be adjusted because the specified frequency may not necessarily be achieved due to stray capacitances at the input and output of the inverter 2, etc. To adjust the initial frequency, connect a variable capacitor 7 in parallel with the capacitor 6 or 6 connected to the output or input of the inverter, and adjust the variable capacitor 7 while checking the oscillation frequency with a frequency counter. It is something.

Problems to be Solved by the Invention However, with such a conventional circuit configuration, 1) a variable capacitor is used to adjust the initial deviation of the frequency to a specified frequency, making it difficult to automate; In addition, the rotating part of the variable capacitor must be fixed to prevent the adjustment value from shifting due to vibration, which naturally increases the adjustment cost. Further, the variable capacitor is an expensive component, and together with the adjustment cost, the cost is high.

One possible method for automating adjustment is to trim capacitor 4 or 5 using a laser or the like without using a variable capacitor, but the trimming capacitor itself is a special component and is technically more difficult than trimming a resistor. Its high cost hindered automation. In addition, as another means of automation, it is possible to measure and determine in advance the capacitor capacity that produces a specified frequency without using a variable capacitor, and then mount a capacitor with that capacity, but in general, highly accurate capacitors are available. This has hindered automation as it is difficult.

Means for Solving the Problems In order to solve the above problems, the frequency adjustment circuit of the present invention has the following features:
A capacitor and a variable capacitance diode are connected in series between the output or input of the inverter and the ground, and a regulating voltage generating means using resistance voltage division is connected to the connection between the capacitor and the variable capacitance diode.

Operation According to the present invention, with the above-described configuration, the initial deviation of the frequency can be adjusted to a specified frequency by adjusting the resistance value of the resistive voltage divider circuit of the adjustment voltage generation circuit.

EXAMPLES Below, the frequency adjustment circuit of the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of a first embodiment of the frequency adjustment circuit of the present invention. In FIG. 1, a broken line 1 indicates a crystal oscillator circuit similar to that described in the conventional example, 10 a DC cut capacitor that prevents DC voltage from being applied to the output of the inverter, and 11 a capacitor that is stabilized by a reverse bias voltage. A variable capacitance diode whose capacitance changes, the broken line portion 12, is a regulating voltage generating means.

The operation of the above configuration will be explained below.

The oscillation frequency of the crystal oscillator circuit 1 is determined by the variable capacitance diode 1
Series capacitance Ct of capacitance Cd of capacitor 1 and capacitance Cc of capacitor 10 (Ct=1/((1/α+(1/Co)
)) is determined. The capacitance Cd of the variable capacitance diode 11 is proportional to 147 in the case of a grade junction (diffusion junction) and to 17af in the case of a step junction (alloy junction).

Therefore, the oscillation frequency can be varied by changing the reverse bias voltage of the variable capacitance diode 11, and the voltage (adjustment voltage Va
) can be adjusted to a specified frequency by supplying it from the adjustment voltage generating means 12.

The adjustment voltage generating means 12 will be explained below.

The regulated voltage Va of the regulated voltage generating means is obtained by dividing a voltage similar to the voltage supplied to the inverter using resistors 13 and 14. The regulated voltage Va is obtained by first obtaining the regulated voltage Va at a specified frequency without mounting the resistor 13.14, and then mounting the resistor 13.14 with the voltage division ratio that will result in the regulated voltage Va. Alternatively, it is determined by a method of trimming the resistor 13 or 14 using a laser or the like.

The second embodiment will be described below with reference to FIG. In FIG. 2, the structure and operation are the same as in the first embodiment described above except for the circuit of the adjustment voltage generating means indicated by the broken line 12, and the explanation thereof will be omitted.

The regulated voltage Va of the regulated voltage generating means in FIG.
R, 2R, 4R, sR resistors 16゜16.17.18
is obtained by dividing the voltage by a resistor 19 with a resistance value of 1R,
After setting the switches 20, 21゜22.23 connected in parallel with the resistors 15, 16, 17゜18, respectively, to generate 16 levels of voltage, and finding the adjusted voltage Va that will give the specified frequency in advance. , the switches 20 and 21
．． This is obtained by setting 22°23.

In both the first embodiment and the second embodiment, an adjustment circuit is connected to the output side of the inverter, but adjustment can be made in the same way even if the adjustment circuit is connected to the input side of the inverter.

Effects of the Invention As described above, the present invention eliminates the need for an expensive variable capacitor and makes it possible to construct an adjustment circuit using inexpensive components. The reverse bias voltage of the capacitor diode is adjusted by the resistance value of the resistor voltage divider circuit, so as a means of automation, it is also possible to adjust the adjustment voltage by mounting a resistor with a resistance value that corresponds to a predetermined adjustment voltage. The means for trimming the resistor to achieve this can also be easily automated, since it can be done using commonly available resistors.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a frequency adjustment circuit according to a first embodiment of the present invention, FIG. 2 is a circuit diagram of a frequency adjustment circuit according to a second embodiment of the present invention, and FIG. 3 is a circuit diagram of a conventional frequency adjustment circuit. It is a circuit diagram. 1... Crystal oscillation circuit, 10... Capacitor, 11... Variable capacitance diode, 12...
... Adjustment voltage generation means. Name of agent: Patent attorney Shigetaka Awano and 1 other person/-
- Mizushina's clever and clever circuit? -゛Inverter 13, 14'・-connection resistance,

Claims (1)

[Claims] In a crystal oscillation circuit consisting of an inverter and a crystal, a capacitor and a variable capacitance diode are connected in series between the output or input of the inverter and the ground, and a regulating voltage generating means is connected to the connection between the capacitor and the variable capacitance diode. Adjustment circuit.