JPH0442601A - Cmos crystal oscillating circuit - Google Patents

Abstract

PURPOSE:To ensure stable oscillation with a wide range of power supply voltage by activating a 1st CMOS transistor (TR) feedback resistor when the power supply voltage is lower than a threshold voltage and activating a 2nd CMOS TR feedback resistor with a different characteristic from the characteristic of the 1st CMOS TR feedback resistor when the power supply voltage is higher than a threshold voltage. CONSTITUTION:The circuit is provided with a crystal resonator 27, an inverter 21 connecting in parallel with the crystal resonator 27, a 1st CMOS TR feedback resistor 22 connected in parallel with the inverter 21 when the power supply voltage is lower than a threshold voltage, and a 2nd CMOS TR feedback resistor 23 connected in parallel with the inverter 21 when the power supply voltage is higher than the threshold voltage. Then a feedback resistor control circuit 26 controls transfer gates 24,25 in response to the power supply voltage Vdd of the oscillating circuit to select the low voltage operating feedback resistor 22 and the high voltage operating feedback reistor 23. Thus, even when the power supply voltage is high or low, almost a constant feedback resistance is obtained and even when the power supply voltage Vdd is fluctuated, stable oscillation is ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a Colpitts type OMO8 (complementary metal oxide semiconductor) crystal oscillation circuit.

[Prior Art] FIG. 4 shows a conventional Colpitts type CMO3 crystal oscillation circuit.

As shown in the figure, an inverter 11 and a feedback resistor 12 are provided inside the CMOS integrated circuit 10. These inverter 11 and feedback resistor 12 are connected to the oscillation input terminal 05CIN and oscillation output terminal 05C of the CMOS integrated circuit IO.
Connected in parallel between OUT.

The oscillation output terminal 08COUT is connected to the internal circuit of the CMO3 integrated circuit 10. A crystal resonator 13 is externally connected to the oscillation input terminal 03CIN and the oscillation output terminal 03COUT. These inverter 11, feedback resistor 1
2 and the crystal resonator 13 constitute a Colpitts-type CMOS crystal oscillation circuit.

Oscillation input terminal 05CIN and oscillation output terminal 08COUT
are connected to load capacitors 14a and 14b, and these load capacitors 14a and 14b are grounded, respectively.

FIG. 5 is a circuit diagram showing the configuration of the feedback resistor 12.

As shown in the figure, the feedback resistor 12 is a CMOS transistor, that is, a P-type FET (field effect transistor) 121.
and the N-type FET 12b.

[Problems to be Solved by the Invention] As described above, in the conventional CMO3 crystal oscillation circuit, the P-type FET 12a and the N-type FET 12 are used as the feedback resistor 12.
Since the on-resistance with b is used, there is a problem in that when the power supply voltage vdd of the oscillation circuit fluctuates, the resistance value of the feedback resistor 12 fluctuates, causing oscillation failure.

Therefore, an object of the present invention is to provide a CMOS crystal oscillation circuit with a simple circuit configuration that ensures stable oscillation operation over a wide range of power supply voltages.

[Means for Solving the Problems] In order to achieve the above-mentioned object, a CMOS crystal oscillation circuit of the present invention includes a crystal resonator, an inverter connected in parallel to the crystal resonator, and a power supply voltage that is set to a predetermined threshold. a first CMOS transistor feedback resistor connected in parallel to the inverter when the supply voltage is lower than the threshold voltage; and a second CMOS transistor feedback resistor connected in parallel to the inverter when the supply voltage is higher than the threshold voltage.
and a transistor feedback resistor.

[Function] When the power supply voltage is lower than a predetermined threshold voltage, the first C
A MOS transistor feedback resistor operates, and when the power supply voltage is higher than a predetermined threshold voltage, a second CMOS transistor feedback resistor operates, which has characteristics different from those of the first CMOS transistor feedback resistor. Therefore, a substantially constant feedback resistance value is obtained whether the power supply voltage is low or high, and as a result, stable oscillation operation is ensured over a wide range of power supply voltages.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a CMOS crystal oscillation circuit according to the present invention.

As shown in the figure, an inverter 21, a feedback resistor 22 for low voltage operation, a feedback resistor 23 for high voltage operation, a transfer gate 24, a transfer gate 25, and a feedback resistance control circuit 26 are provided inside the CMO3 integrated circuit 20. ing. The feedback resistor 22 for low voltage operation and the feedback resistor 23 for high voltage operation are examples of the first CMOS transistor feedback resistor and the second CMOS transistor feedback resistor of the present invention, respectively.

The feedback resistor 22 for low voltage operation and the transfer gate 24 are connected in series, and the feedback resistor 23 for high voltage operation and the transfer gate 25 are connected in series.

The low voltage operation feedback resistor 22 connected in series with the inverter 21 and the high voltage operation feedback resistor 23 and transfer gate 25 connected in series with the transfer gate 24 are the oscillation input terminal O8CAM and the oscillation output terminal 09COUT of the CMOS integrated circuit 20. are connected in parallel between.

The oscillation output terminal 03COUT is connected to the internal circuit of the CMO3 integrated circuit 20.

The crystal resonator 27 is externally connected to the oscillation input terminal 03CIN and the oscillation output terminal 05COUT. These inverter 21, feedback resistor 22 for low voltage operation, feedback resistor 23 for high voltage operation, and crystal resonator 27 constitute a CMOS crystal oscillation circuit.

Oscillation input terminal 03CIN and oscillation output terminal 03COUT
The load capacity is 28! and 28b are connected, and the other ends of these load capacitors 28a and 28b are grounded.

FIG. 2 is a circuit diagram showing the configuration of the feedback resistor 22 for low voltage operation, and FIG. 3 is a circuit diagram showing the configuration of the feedback resistor 23 for high voltage operation.

As shown in these figures, the feedback resistor 22 for low voltage operation consists of CMOS transistors, that is, a P-type FET 22a and an N-type FET 22a.
The feedback resistor 23 for high voltage operation is composed of the on-resistance of the ET22b and the P-type FET23a and the N-type FET2.
It is configured similarly to the feedback resistor 22 for low voltage operation due to the on-resistance with 3b.

Next, the operation of the above embodiment will be explained.

In FIG. 1, the feedback resistance control circuit 26 detects the power supply voltage Vdd of the oscillation circuit, and controls the transfer gates 24 and 25 as follows.
The feedback resistor 22 for low-voltage operation and the feedback resistor 23 for high-voltage operation are switched accordingly.

That is, when the detected power supply voltage vdd is less than a predetermined threshold voltage VT, a control signal SLV is generated to turn on the transfer gate 24, and a control signal 5llv is generated to turn off the transfer gate 25.

On the other hand, when the power supply voltage Vdd is higher than the threshold voltage VT, a control signal SHY is generated to turn on the transfer gate 25, and a control signal SLV is generated to turn off the transfer gate 24.

This threshold voltage■. is a value that depends on the oscillation frequency of the crystal resonator and the range of the power supply voltage V0;
Using a 3kHz crystal oscillator, the power supply voltage Vdd is approximately IV
The threshold voltage vT in the range from about 3V to about 6V can be set to about 3V to about 3.5V. The resistance values of the feedback resistor 22 for low voltage operation and the feedback resistor 23 for high voltage operation, which are switched as described above, are P type FET 22a and N for the feedback resistor 22 for low voltage operation.
It is determined by the on-resistance setting of type FET22b, and
The feedback resistor 23 for high voltage operation is a P-type FET 23a.
It is determined by the on-resistance setting of the N-type FET 23b,
The value is approximately constant in each operating voltage range, that is, approximately 10 MΩ in this example.

Therefore, according to this embodiment, the feedback resistance control circuit 26 controls the transfer gate 2 in accordance with the power supply voltage vdd of the oscillation circuit.
4 and 25 to switch the feedback resistor 22 for low voltage operation and the feedback resistor 23 for high voltage operation, a nearly constant feedback resistance value can be obtained whether the power supply voltage is low or high. Stable oscillation operation is ensured even if vdd fluctuates.

[Effects of the Invention] As explained above, the present invention includes a crystal resonator, an inverter connected in parallel to the crystal resonator, and an inverter connected in parallel to the inverter when the power supply voltage is lower than a predetermined threshold voltage. The first CMOS transistor feedback resistor is connected in parallel to the inverter when the power supply voltage is higher than a predetermined threshold voltage, so it is stable over a wide range of power supply voltages. oscillation operation can be ensured.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the CMOS crystal oscillation circuit according to the present invention, FIG. 2 is a circuit diagram showing the configuration of the feedback resistor for low voltage operation shown in FIG. 1, and FIG. A circuit diagram showing the configuration of a feedback resistor for high voltage operation, Figure 4 is a circuit diagram showing a conventional Colpitts type CMOS crystal oscillation circuit, and Figure 5 is
FIG. 3 is a circuit diagram showing the configuration of the feedback resistor shown in the figure. 21... Inverter, 22... Feedback resistor for low voltage operation, 23... Feedback resistor for high voltage operation, 22a, 23B... P-type FET, 2
2b, 23b...N-type FET, 24.25
...Transfer gate, 26...Feedback resistance control circuit, 27...Crystal resonator, 28a
, 28b/old...Load capacity. Figure 1 Figure 2 Figure 3 rllJ

Claims (1)

[Claims] a crystal resonator; an inverter connected in parallel to the crystal resonator; a first CMOS transistor feedback resistor connected in parallel to the inverter when the power supply voltage is lower than a predetermined threshold voltage; a second CMOS transistor feedback resistor connected in parallel to the inverter when the inverter is higher than the threshold voltage.