JPS6286907A - Crystal oscillation circuit - Google Patents

Abstract

PURPOSE:To obtain stable oscillation frequency quickly to switching of a MOS transistor by connecting a connection point of capacitors for temperature compensation and to MOS transistor that controls the capacitor and a point of fixed DC potential by the MOS transistor. CONSTITUTION:Plural capacitors C1, C2,...Cn for temperature compensation are connected to a gate terminal of a crystal oscillation circuit, and MOS transistors of N channels TN1, TN2...TNn are connected between other terminals of capacitors and ground. When change of temperature is detected by a temperature sensor 9, data 7m that makes an arbitrary capacitor Cm (m is an arbitrary natural number, m<=n) from on to off is sent correspondingly. Then, an N channel MOS transistor TNm becomes off state, and at the same time, a P channel MOS transistor TPm becomes off state, and the DC level of drain of the TNm becomes equal to that of the gate of the oscillating circuit. Therefore, capacitance of a parasitic diode by the N channel MOS transistor TNm becomes constant at once.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an excavation circuit for a temperature compensated crystal oscillation circuit.

[Summary of the invention]

The present invention provides a temperature-compensated crystal oscillator comprising a plurality of temperature-compensating capacitors connected in series between the gate terminal or drain terminal of an oscillator circuit and ground or a power supply, and a MOS transistor for controlling the on-off of the capacitors. In the circuit, the connection point between the capacitor and the MoS transistor and the point where the DC potential is constant are M
(Mo8) The transistor operates in the opposite direction to the on-off operation of the transistor and controls the capacitor. (Mo8) The transistor controls the DC level of the parasitic diode caused by the off state of the transistor. , the stability of the oscillation frequency is improved by maintaining a certain constant DC level.

[Conventional technology]

A conventional crystal oscillation circuit having a temperature compensation circuit using a capacitor has a temperature compensation capacitor, C8°C7...0n, at the gate terminal of the crystal oscillation circuit, as shown in Figure 45.
(n is a natural number) is connected, and the capacitor CI m
Mo8 transistor TN1... is connected in series to C2...On. TN2...TNn is connected,
Control data 71 * 7 in temperature report 6sw controller 8 sent from temperature sensor 9!・・・・・・7
n, and the MoS transistors TNI, TN2・
...by controlling TNn), temperature compensation was performed.

[Problem that the invention seeks to solve]

However, in the conventional crystal oscillation circuit having a temperature compensation circuit using a capacitor, when the Mo8 transistor TN is turned off, a parasitic diode is created due to the structure of the Mo8 transistor. Figure 1 shows a conventional circuit diagram with a parasitic diode.

The DC level applied to the diode 10 is determined by the structure of the semiconductor, and the leakage current 11 to (g) and (-)
M
OFI) Even if the transistor TN is switched back from the on state to the off state, it takes time for the capacitance of the capacitor C8 and the diode 10 to be charged to the above DC level by the leakage current 11, and the capacitance bond of the diode decreases. Since the oscillation frequency of the crystal oscillation circuit is not stable immediately, the oscillation frequency of the crystal oscillation circuit is not stable.

[Means for solving problems]

A plurality of temperature compensation capacitors connected in series between the gate terminal or drain terminal of the oscillation circuit and the ground or the power source, and a Mo for controlling the on-off of the capacitors.
In a temperature compensated crystal oscillator circuit composed of S transistors, a connection point between the capacitor and the MOS transistor, and a point at which a DC potential is determined are connected by an Mo8 transistor, and the MOS transistor i)',
It is characterized in that the MoS transistor that controls the balance has an on/off operation that is opposite to its on/off operation.

[Effect]

According to the above configuration of the present invention, a parasitic diode is formed when the Mo8 transistor that controls the temperature compensation capacitor is turned off, but the Mo8 transistor connected in parallel to the capacitor is not turned on.
Since the DC level of the parasitic diode is equal to a certain fixed DC level, a stable frequency can be obtained.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. ′
XfA+ As shown in the figure, a plurality of temperature compensation capacitors C, a, νcn are connected to the gate terminal of a crystal oscillation circuit, and an N-channel Mo8 transistor TNI is connected between the other terminal of the capacitor and ground.

TN2...TNn is connected. Also, the aforementioned Conde 7? P-channel MOS transistors TPI, TP2...... are connected in parallel to C,, C,...On.
TPn is connected. 1 is a feedback resistor, 2 is an oscillation inverter, 5 is a crystal oscillator, 4 is a drain resistor, 5 is a gate capacitance, 6 is a drain resistor, 7, 1.7.・・・・・・7n
is M, a signal that controls the OS transistor; 8 is a SW controller that outputs control data corresponding to temperature; 9
is a temperature sensor. Assuming that the temperature sensor 9 senses a change in temperature, the data that changes an arbitrary capacitor Cm (m is any natural number m≦n) from on to off (from H level to L level) When 7m is sent, the N-channel MOS transistor T Nm turns off and the P-channel MOS transistor TPm turns off at the same time, and the DC level of the drain of TNm becomes the same as the gate of the oscillation circuit, so the N-channel 1111OS The electrostatic capacitance of the parasitic diode caused by the transistor TNm quickly becomes constant.

Figure 2 shows another embodiment of the invention. The MOS transistor TP is connected to the (g) power supply, and a similar effect can be obtained.

In the embodiment shown in FIG. 1, the TN is N channel Mo8
The transistors are configured with TP and P-channel MO8 transistors, but by inverting the control signals, TN can be replaced with P-channel MO8 transistors and TP.
In the embodiment shown in Figure 1, the temperature compensation capacitor is connected to the gate side of the oscillation circuit, but if it is connected to the drain side of the oscillation circuit, But you can get the same effect.

〔Effect of the invention〕

As described above, the present invention has a structure in which the connection point of a temperature compensation capacitor and a MOS transistor that controls the capacitor is connected by a MOS transistor to a point where a DC potential is fixed. When the MOS transistor that controls the capacitor is turned off, the DC level of the parasitic diode that is created immediately becomes constant.
This has the effect of quickly providing a stable oscillation frequency for the switching of the OS transistor.

Figure \ is a diagram of a conventional temperature compensated crystal oscillation circuit.

Figure 1 shows a conventional circuit with a parasitic diode.
figure.

1...Returning resistance 2...Oscillating inverter 5...Crystal oscillator 4...Drain resistance 5...Gate capacitance 6,...Drain capacitance 71 e 7t...7n ・...Control signal C
,,O,...On...Temperature compensation capacitor TPI, TP2...TPn...P channel MOS transistor TNI, TN2...TNn...N channel MO8 transistor or more

Claims (1)

[Claims] A CMOS crystal oscillation circuit comprising at least one temperature compensation capacitor connected in series between the gate terminal or drain terminal of the oscillation circuit and the ground or + power supply, and a MOS transistor for controlling the capacitor on and off. , the capacitor and the M
A MOS transistor connects the connection point of the OS transistor and a point where the DC potential is fixed, and the MOS transistor connected to the point where the DC potential is fixed turns on and off the MOS transistor that controls the capacitor. A crystal oscillation circuit characterized by operating in the opposite direction.