JPH03155206A - Oscillator circuit - Google Patents

Abstract

PURPOSE:To improve the characteristic of a high accuracy oscillator by providing a 1st capacitor connecting to the input and a 2nd capacitor connecting to the output to an inverse amplifier and varying the 1st and 2nd capacitors simultaneously to adjust the oscillation frequency. CONSTITUTION:A 1st capacitor 6 connecting to the input and a 2nd capacitor 7 connecting to the output are provided to an inverse amplifier 3, and the oscillating frequency is adjusted so as to vary the 1st capacitor 6 and the 2nd capacitor 7 simultaneously thereby adjusting the oscillating frequency. Thus, the oscillating frequency automatically range is widened with less variable capacitance and the operating current of the oscillation circuit due to the increase in the drain capacitance is minimized without much sacrificing the oscillation start characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for adjusting the oscillation frequency of a high-precision oscillator in the communication field and the like.

[Conventional technology]

The oscillation frequency adjustment of conventional crystal oscillation circuits has been carried out using variable drain capacitance or variable gate capacitance as shown in FIG. 2 from the viewpoint of oscillation stability and ease of adjustment. 1 is a crystal resonator, 2 is an oscillation feedback resistor, 3 is an inverting amplifier, 4 is a gate signal of the inverting amplifier, 5 is a drain signal, 20 is a gate capacitance, 21 is a variable drain capacitor, and a capacitance variable device 2
2, the drain capacitance 21 is changed to adjust the oscillation frequency.

As a normal characteristic, the oscillation frequency decreases in proportion to the reciprocal of the drain capacitance, and a reasonable frequency variable range of ±50 [PPM] to ±100 [PPM] is required as a required specification.

[Problem to be solved by the invention]

However, in the conventional system, in order to widen the frequency variable range, the variable range of the drain capacitance (or gate capacitance) must also be widened.

Therefore, ■The value of the variable capacitance is large, making it a large component, making it difficult to make the oscillator smaller and lighter.

■If the drain capacitance (or gate capacitance) becomes too large, oscillation itself becomes difficult to occur, making it difficult to operate at low voltage (for example, battery-driven).

■If the drain capacitance becomes too large, the output charging/discharging current of the inverting amplifier will be I a ``f aac '' ``D ' c.

Since this is almost proportional to the drain capacitance, there have been problems such as an increase in the current consumption of the oscillation circuit.

In order to overcome the above-mentioned problems, the present invention expands the oscillation frequency adjustment range with a smaller variable capacitance value than the conventional one, does not significantly sacrifice the oscillation start-up performance, and also increases the operating current of the oscillation circuit due to the increased drain capacitance. The aim is to suppress as much as possible.

[Means to solve the problem]

The crystal oscillation circuit of the present invention has a first capacitor connected to the input side of an inverting amplifier and a second capacitor connected to the output side, and changes the first capacitance and the second capacitance simultaneously. It is characterized in that the oscillation frequency is adjusted by this.

〔Example〕 FIG. 1 shows a crystal oscillation circuit of the present invention.

1 is a crystal oscillator, 2 is a feedback resistor, 3 is an inverting amplifier, 4 is a gate signal of the inverting amplifier, 5 is a drain signal of the inverting amplifier, 6 and 7 are variable gate capacitance, variable drain capacitance,
The capacitance level is determined by the control signal 8 from the capacitance variable device 9, and the gate capacitance and drain capacitance are changed simultaneously by the same amount.

The details of FIG. 1 will be explained in detail.

FIG. 3 is a diagram that best represents the characteristics of the present invention, and is a diagram showing the frequency fluctuation characteristics due to capacitance changes. When the gate capacitance change value is 8CG and the drain capacitance change value is ΔCo, the correlation between the frequency change value Δ((lj is on the order of [PPMI)] and the sum of the capacitance changes ΔC(-ACG+ΔCo) Curve 25 shows this.If the gate capacitance is fixed and only the drain capacitance is variable, the sum of the capacitance changes will be CD, and the frequency curve will be 26. When compared with the same value of △C, the oscillation circuit of the present invention has 4 to 5 times the slowing and fastening characteristics, indicating that the frequency adjustment range can be wider. The amount of change in capacitance ΔC is 1/4 to 1 compared to the variable capacitance method.
With a small value of 15, it is possible to obtain the frequency adjustment range that was conventionally required.

Next, let's list some of the advantages of having a small variable capacitance value.

FIG. 4 shows an example of drain capacitance-oscillation current consumption characteristics, which are common characteristics in crystal oscillation circuits. The vertical axis shows the rate of increase in current consumption, and the amount of change in drain capacitance ΔCo = O[
It is expressed as a relative value with the time of PF] being 0 [%]. Since an increase in gate capacitance has a very small effect on current consumption compared to an increase in drain capacitance, it is possible to suppress an increase in current consumption by using the oscillation circuit of the present invention.

FIG. 5 shows the sum of gate capacitance and drain capacitance variation versus oscillation start voltage characteristic. The vertical axis is a relative value with 8C-0 [PF] being 0 [%].

From this, the less 80, the lower the oscillation start voltage and the better the oscillation start-up performance.

In this embodiment, a crystal resonator has been described, but similar characteristics can be obtained with a resonator such as a ceramic resonator, and the present invention is effective.

Further, as for the configuration of the capacitance variable device 9 shown in FIG. 1, a trimmer capacitor is used for boat fishing, but a barrier pull capacitor using voltage control or the like is also applicable.

Next, an example in which the present invention is formed on a semiconductor integrated device will be shown.

FIG. 6 shows an oscillation frequency adjustment circuit using a simultaneous variable gate/drain capacitance method in a MOS type semiconductor integrated device. The most characteristic part of this is that N
The circuit that turns on the type transistor, the divided gate capacitance (70, 71, 72, 73) of cao-cci, and the CDo
"" Cl) 3 divided drain capacitance (74, 75, 76
, 77), and the divided gate capacitance and the divided drain capacitance are simultaneously changed by the same amount by the digital signal.

Now, if we set the capacitance value as CGO-CDO-1 [PF] Cat-C3l-2 [PF] CO2-CD2-4 [PF] Ca1-Co3”8 [PF], the gate capacitance ffi (CG)
, Drain Yong! The value of (CD) becomes the following function by DO-D3.

Ca = Do +2D1 +402+8Di [PF
lCD-Do + 2 D + + 4 D2 + 8
D3 [P F ] However, the signal is “H” for DO to D3.
”, the value is 1, and when the signal is “Lo”, the value is 0.

Therefore, with 4 bits of digital signal, Ca and Co are 1 to 1.
It is possible to change up to 1 [PF] up to 5 [PF] at the same time. Therefore, the output signal 55 has a frequency-adjusted sine waveform.

Further, the values of the gate capacitance and the drain capacitance do not have to be the same each, and may be changed according to the characteristics of the vibrating body.

-For boat fishing, the drain capacity should be slightly larger, and Co+-
Oscillation stability is further improved when the value is set to about 1,2Cc+(i-0,1,2,3).

〔Effect of the invention〕

As described above, the oscillation circuit of the present invention can widen the frequency variable range with a smaller variable capacitance value than the conventional variable drain capacitance method (or variable gate capacitance method), and can be used as a high-precision oscillator. Characteristics increase.

Furthermore, being able to reduce the variable capacitance value produces the following advantages.

First, it suppresses the increase in oscillation current consumption, helping to reduce the power of the oscillator.

The power supply voltage required for oscillation is also low, and the start-up performance as an oscillator is improved, making the oscillator more suitable for low-voltage drive such as batteries.

Furthermore, when integrated into a semiconductor, since the total capacitance is small, the area of the oscillation circuit can be reduced, and the degree of integration as a semiconductor can be increased.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an oscillation circuit using a simultaneous variable gate/drain capacitance method according to the present invention. FIG. 2 is a diagram showing an oscillation circuit using a conventional variable drain capacitance method. FIG. 3 is a diagram of the change in oscillation frequency with respect to the amount of change in oscillation capacitance. FIG. 4 is a diagram of the oscillation current consumption depending on χ·I when the drain capacitance changes. FIG. 5 is a diagram of oscillation start voltage with respect to the amount of change in oscillation capacitance. FIG. 6 is a diagram of an oscillation circuit of the present invention applied to a semiconductor integrated circuit. 1... Crystal resonator 2... Oscillation feedback resistor 3... Inverting amplifier 6... Gate side variable capacitor 7... Drain side variable capacitor 8... Gate capacitance and drain capacitance variable control signal 9.・Capacity variable device or more -20] 20 Figure Figure 'ilQ 0 Figure

Claims (1)

[Claims] In an oscillation circuit, having a first capacitor (capacitor) connected to the input side of an inverting amplifier and a second capacitor connected to the output side, and changing the first capacitance and the second capacitance simultaneously. An oscillation circuit characterized in that the oscillation frequency is adjusted by.