JP2014143454A - Crystal oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal oscillation circuit that allows reducing power consumption compared to conventional general crystal oscillators.SOLUTION: A crystal oscillation circuit 100 includes a first inverter 1, a first crystal resonator 2, a second inverter 3, and a second crystal resonator 4. The crystal oscillation circuit 100 has a circuit configuration in which the first inverter 1, the first crystal resonator 2 for clock generation, the second inverter 3, and the second crystal resonator 4 for clock generation are connected in series.

Description

  The present invention relates to a crystal oscillation circuit using a crystal resonator.

One common crystal oscillator is a single-stage Pierce oscillator.
oscillator) is known. As shown in FIG. 4, the conventional single-stage Pierce oscillator 300 includes an inverter 301 provided between a source voltage line Vss to which a voltage of +1.8 V is applied and a ground line GND, and an inverter 301. A crystal oscillator 302 for clock generation connected in parallel via a resistor R, a load capacitor 303 for charging / discharging provided between an input node 317 of the inverter 301 and the ground line GND, and an output of the inverter 301 A charge / discharge load capacitor 304 provided between the node 318 and the ground line GND via a resistor R.

Another conventional crystal oscillator is the two-stage Pierce oscillator (2-stages Pierce).
oscillator) is known. As shown in FIG. 5, a conventional two-stage Pierce oscillator 400 is an oscillator in which an inverter, a capacitor, an inverter, and a crystal resonator are connected in series, and a source voltage to which a voltage of +1.0 V is applied. A first inverter 401 provided between the line Vss and the ground line GND; a second inverter 402; and a noise removing block capacitor 403 connected in series between the first inverter 401 and the second inverter 402. The charge / discharge load capacitor 404 provided between the input node 417 of the first inverter 401 and the ground line GND, and between the input node 417 of the first inverter 401 and the output node 418 of the second inverter 402. And a crystal oscillator 405 for clock generation provided. As another example of an oscillator in which an inverter, a capacitor, and a crystal resonator are connected in series, a crystal oscillator shown in the following Patent Document 1 (see FIG. 1) has been proposed.

JP 2009-124290 A

  However, the above-described conventional general crystal oscillator has a problem in that power consumption increases due to accumulation of extra charges in each capacitor, which is an essential component.

  Accordingly, an object of the present invention is to provide a crystal oscillation circuit capable of reducing power consumption as compared with a conventional general crystal oscillator.

(1) A crystal oscillation circuit according to the present invention includes a first inverter connected between a first voltage line and a second voltage line, and a first crystal vibration having one end connected to an output node of the first inverter. A second inverter connected to the other end of the first crystal unit, one end connected to the output node of the second inverter, and the other end connected to the input node of the first inverter. And a second crystal resonator.

  According to the configuration of (1) above, the first inverter, the first crystal resonator, the second inverter, and the second crystal resonator are connected in series, so that the configuration is essential for the conventional general crystal oscillator A crystal oscillation circuit can be configured without using each capacitor as an element. Therefore, unlike the conventional general crystal oscillator, no extra charge is accumulated in each capacitor. As a result, power consumption can be reduced as compared with a conventional general crystal oscillator.

(2) In the crystal oscillation circuit of (1), each inverter includes a first transistor having a gate connected to the input node, a source connected to the first voltage line, and a drain connected to the output node. A second transistor having a gate connected to the input node, a source connected to the second voltage line, a drain connected to the output node, one end connected to the input node, and the other end connected to the output node And a resistance for feedback.

  According to the configuration of (2) above, a crystal oscillation circuit capable of reducing power consumption compared with a conventional general crystal oscillator by configuring each inverter with a first transistor, a second transistor, and a resistor. Can be configured easily.

1 is a circuit diagram of a crystal oscillation circuit 100 according to an embodiment of the present invention. FIG. 2 is a block diagram showing a circuit configuration inside an inverter of a crystal oscillation circuit 200 as an example of the crystal oscillation circuit 100 shown in FIG. 1. It is explanatory drawing which shows the simulation result using the prototype of the crystal oscillation circuit. 1 is a circuit diagram of a conventional single-stage Pierce oscillator 300. FIG. FIG. 6 is a circuit diagram of a conventional two-stage Pierce oscillator 400.

  Hereinafter, a crystal oscillation circuit according to an embodiment of the present invention will be described with reference to FIGS.

(Whole structure of crystal oscillation circuit)
As shown in FIG. 1, the crystal oscillation circuit 100 according to the present embodiment includes a first inverter 1, a first crystal resonator 2, a second inverter 3, and a second crystal resonator 4. It is. The crystal oscillation circuit 100 has a circuit configuration in which a first inverter 1, a first crystal oscillator 2 for generating a clock, a second inverter 3, and a second crystal oscillator 4 for generating a clock are connected in series. It is what you have.

(Example of crystal oscillation circuit)
FIG. 2 is a block diagram showing a circuit configuration inside inverters 21 and 23 of crystal oscillation circuit 200 as an example of crystal oscillation circuit 100 shown in FIG. As shown in FIG. 2, the inverters 21 and 23 have the same circuit configuration, and therefore the same reference numerals are given to the respective components.

  As shown in FIG. 2, the first crystal resonator 22 has one end connected to the output node 18 of the first inverter 21 and the other end connected to the input node 17 of the second inverter 23. Similarly, the second crystal resonator 24 has one end connected to the output node 18 of the second inverter 23 and the other end connected to the input node 17 of the first inverter 21. Hereinafter, the first inverter 21 and the second inverter 23 may be abbreviated as each inverter. Similarly, the first crystal unit 22 and the second crystal unit 24 may be abbreviated as each crystal unit.

(Configuration of each inverter)
As shown in FIG. 2, the first inverter 21 and the second inverter 23 include the first transistor 10, the second transistor 11, the first diode 12, the second diode 13, the third diode 14, and the fourth transistor. A diode 15 and a feedback resistor 16 are provided. Hereinafter, the first diode 12, the second diode 13, the third diode 14, and the fourth diode 15 may be abbreviated as each diode.

  The first transistor 10 and the second transistor 11 function as a P-channel MOS transistor and an N-channel MOS transistor whose on / off is opposite to each other. A combination of two transistors 11 constitutes a complementary metal oxide semiconductor (CMOS) circuit.

  The gate of the first transistor 10 is connected to the input node 17 of each inverter and receives an input signal (IN) from each crystal resonator. The source of the first transistor 10 is connected to a source voltage line Vss (first voltage line) to which a voltage of +1 V is applied. The drain of the first transistor 10 is connected to the output node 18 of the first transistor 10 and outputs an output signal (OUT) to each crystal resonator.

  The gate of the second transistor 11 is connected to the input node 17 of each inverter and receives an input signal (IN) from the second crystal unit 4. The source of the second transistor 11 is connected to the ground line GND (second voltage line). The drain of the second transistor 11 is connected to the output node 18 of each inverter, and outputs an output signal (OUT) to each crystal resonator.

  Each of the diodes 12 to 15 is provided to protect the first transistor 10 and the second transistor 11 from being destroyed by static electricity.

  One end of the first diode 12 is connected to the input node 17 (the gates of the first transistor 10 and the second transistor 11) of each inverter, and the other end is connected to the source voltage line Vss (the source of the first transistor 10). It is connected. As a result, current flows only in the direction from the input node 17 toward the source voltage line Vss.

  One end of the second diode 13 is connected to the input node 17 (the gates of the first transistor 10 and the second transistor 11) of each inverter, and the other end is connected to the ground line GND (the source of the second transistor 11). It is what has been. As a result, the current flows only in the direction from the ground line GND toward the input node 17.

  One end of the third diode 14 is connected to the output node 18 (each drain of the first transistor 10 and the second transistor 11) of each inverter, and the other end is connected to the source voltage line Vss (the source of the first transistor 10). It is connected. Thereby, the current flows only in the direction from the output node 18 toward the source voltage line Vss.

  The fourth diode 15 has one end connected to the output node 18 of each inverter (the drains of the first transistor 10 and the second transistor 11), and the other end connected to the ground line GND (the source of the second transistor 11). It is what has been. As a result, the current flows only in the direction from the ground line GND toward the output node 18.

  Note that the capacitance of each diode is preferably at least 0.8 pF or less in order to maintain the performance for protecting the breakdown due to static electricity. As a result, a circuit can be configured using a diode having a capacitance smaller than the capacitance of the capacitor (more specifically, 6 pF to 100 pF), which is an essential component of the conventional general crystal oscillator. Power consumption can be reduced compared to a simple crystal oscillator.

  The resistor 16 is provided to cause regular voltage fluctuations by feeding back a part of the output signal (OUT) of each inverter to the input node 17.

  One end of the resistor 16 is connected to the input node 17 (the gates of the first transistor 10 and the second transistor 11) of each inverter, and the other end is connected to the output node 18 (the first transistor 10 and the second transistor) of each inverter. 11 drains).

  Next, the present invention will be described specifically by way of examples. The inventor performed a simulation of the oscillation operation of the crystal oscillation circuit 200 with respect to the circuit configuration shown in FIG. In addition, this invention is not limited to a present Example.

FIG. 3 shows a simulation result of the oscillation operation when a voltage of 0.9 V is applied to the source voltage line Vss. FIG. 3A shows the voltage level V _OUT (V) of the output signal (OUT) output from the output node 18 of the first inverter 21. FIG. 3B shows the voltage level V _IN (V) of the input signal (IN) input to the input node 17 of the first inverter 21.

  In the present embodiment, as shown in FIG. 3B, it has been found that the signal waveform of the input signal (IN) can be made closer to a rectangular wave signal than a sine wave signal. As a result, it is possible to reduce a crowbar current that causes a reduction in switching speed as compared with a conventional general crystal oscillator, and it is possible to make the crystal oscillation circuit 100 with a high power supply voltage without reducing excess current. It was found that it can oscillate. Further, as shown by the arrows in FIG. 3A, at the time when the maximum amplification gain is obtained (near 45.75 (ms) and 45.77 (ms)), it rises from the sine wave signal. Turned out to be faster.

(Experimental results for verifying simulation results)
Table 1 shown below shows an example of an experimental result for verifying the correctness of the simulation result. The inventor verified the oscillation operation when a voltage of 1.4 V to 3.4 V was applied to the source voltage line Vss in the prototype of the crystal oscillation circuit 200 according to the present embodiment. Table 1 shows experimental results when a voltage of 1.5 V is applied to the source voltage line Vss.

  Of each parameter item in Table 1, “vibration frequency”, “vibration frequency in STD (standard circuit)”, “change in operating characteristics over long period (100 hours)”, “HC at 1.5 V (high Speed CMOS type) Inverter power consumption, “rise time required for warming up the crystal unit”, and “rise time from the off state” were similar to those of a conventional general crystal oscillator.

  However, among the items of the parameters in Table 1, the value of “−10 ppm / V” is shown for “Frequency voltage coefficient per unit voltage in the input / output signal of the inverter”. As a result, it has been found that it can be maintained at a value smaller than the frequency change rate in the conventional single-stage Pierce oscillator 300 (see FIG. 4), and it has been found that the signal level in the input / output signal of the inverter can be stabilized.

Table 2 shown below shows another example of the experimental result for verifying the correctness of the simulation result. The present inventor uses the configuration of a German foundry company (L Foundry) to oscillate when a voltage of 1.0 V is applied to the source voltage line Vss in an extremely low power consumption type RTC (Real Time Clock). Was verified.

  Among the parameter items, for “power consumption at 1.0 V”, a value of 0.2 to 0.5 μW is obtained, and can be suppressed to a value smaller than the value of the mass-produced product (> 1.35 μW). There was found. Moreover, it turned out that it can suppress to a value smaller than the numerical value (0.5-1.0 microwatt) reported by the report of another researcher. More specifically, it has been found that the power consumption can be reduced to about 1/5 (about 0.3 μW) of the power consumed by a conventional general crystal oscillator (1.5 μW).

(Practical merit of crystal oscillation circuit)
Tables 3 and 4 below show ASIC (Application
This shows a practical merit of the crystal oscillation circuit 200 according to the present embodiment mounted as a specific integrated circuit). “Class 6” shown in the components in Tables 3 and 4 is the design class of the most commonly used 0.13 mm pitch printed circuit board (PCB) among the printed circuit boards (PCB). Is shown.

Regarding each item of the components in Tables 3 and 4, when the crystal oscillation circuit 200 according to the present embodiment and the conventional two-stage Pierce oscillator 400 (see FIG. 5) are compared, The area of the active region in the circuit (cm ² ) ”is 0.018 (cm ² ), and the“ number of integrated circuit pads / unit completed product ”is 8, which is the same as the conventional two-stage Pierce oscillator 400 .

  However, among the items, “the number of load capacitors” and “the number of DC block capacitors” are both 1 in the conventional two-stage Pierce oscillator 400, and the load capacitor and the DC block capacitor are essential. In contrast, in the crystal oscillation circuit 200 according to the present embodiment, the “number of load capacitors” and the “number of DC block capacitors” are both 0, and the load capacitor and the DC block capacitor are indispensable. It is not a component. Accordingly, it has been found that the cost of the load capacitor and the DC block capacitor can be saved to 0 dollars ($).

  Among the items, in “battery capacity (used for 10 years, lithium ion battery)”, the capacity (energy amount) in the crystal oscillation circuit 200 according to the present embodiment is 50 mWh, and the conventional single-stage Pierce oscillator 300 (see FIG. 4), the capacity (energy amount) (= 0.5 Wh) can be reduced to 1/10, and the conventional two-stage Pierce oscillator 400 (see FIG. 5) capacity (energy amount) (= 0. It was found that it can be reduced to 1/3 of 15 Wh).

Further, among the items, in “area occupied by printed circuit board (PCB) and assembly parts (cm ² ), class 6”, the area of the crystal oscillation circuit 200 according to the present embodiment is 0.4 (cm ^2). And the printed circuit board (PCB) in the crystal oscillation circuit 200 according to the present embodiment can be reduced to 1/10 or less of the area (5 cm ² ) in the single-stage Pierce oscillator 300 and the two-stage Pierce oscillator 400. $ 0.92 compared to the cost of assembled parts ($ 0.08) compared to the cost of printed circuit boards (PCB) and assembled parts ($ 1.00) in single stage Pierce oscillator 300 and two stage Pierce oscillator 400 It turns out that you can only save.

  In addition, as shown in “total price (dollar)” among the items, the total price ($ 1.606) in the crystal oscillation circuit 200 according to the present embodiment is the total price in the single-stage Pierce oscillator 300. Compared to ($ 1.896), the price was reduced by $ 0.29, and compared with the total price ($ 2.111) in the two-stage Pierce oscillator 400, the price was reduced by $ 0.505.

  As a result, it has been found that the crystal oscillation circuit 200 according to the present embodiment is suitable for a battery power supply type or energy storage type system. In particular, the price of the crystal oscillation circuit 200 according to the present embodiment can be kept low by combining long-term durability, inexpensive LSI (Large Scale Integration) technology, and expensive PCB (printed circuit board) technology. Turned out to be possible. Further, since the crystal oscillation circuit 200 according to the present embodiment is a low power consumption type oscillation circuit, it has been found that the battery life can be increased by 3 to 6 times compared to a conventional general crystal oscillator.

(Characteristics of crystal oscillation circuit according to this embodiment)
According to the above configuration, the first inverter 1, the first crystal resonator 2, the second inverter 3, and the second crystal resonator 4 are connected in series, so that the configuration is essential for a conventional general crystal oscillator. The crystal oscillation circuit 100 can be configured without using each capacitor as an element. Therefore, unlike the conventional general crystal oscillators 300 and 400 (see FIGS. 4 and 5), no extra charge is accumulated in each capacitor. As a result, power consumption can be reduced as compared with the conventional general crystal oscillators 300 and 400.

  Further, according to the above configuration, each inverter 21 and 23 is configured by the first transistor 10, the second transistor 11, the diodes 12 to 15, and the resistor 16, so that it consumes more than a conventional general crystal oscillator. The crystal oscillation circuit 200 capable of reducing power can be easily configured.

  Further, according to the above configuration, in the simulation result using the prototype of the crystal oscillation circuit 200, “Frequency voltage coefficient per unit voltage in the input / output signal of the inverter” is −10 ppm / V. As shown, it can be maintained at a value smaller than the frequency change rate in the conventional single-stage Pierce oscillator 300 (see FIG. 4). Therefore, the signal levels of the input / output signals of the inverters 21 and 23 can be made more stable than those of the conventional single-stage Pierce oscillator 300.

  In addition, according to the above configuration, each of the inverters 21 and 23 is more than the capacitance (more specifically, 6 pF to 100 pF) of the capacitor that is an essential component in the conventional general crystal oscillators 300 and 400. Since it is configured using the diodes 12 to 15 having a small capacity (more specifically, <1.6 pF), the power consumption of the crystal oscillation circuit 200 is reduced as compared with the conventional general crystal oscillators 300 and 400. be able to.

  As mentioned above, although embodiment of this invention was described based on drawing, it should be thought that a specific structure is not limited to these embodiment. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent. For example, the crystal oscillation circuit 200 shown in FIG. 2 is shown as an example of the crystal oscillation circuit 100 shown in FIG. 1. However, the present invention is not limited to this, and the present invention has the same effects as the crystal oscillation circuit 100. A crystal oscillation circuit in which the configuration of the crystal oscillation circuit 100 is appropriately changed may be used.

1, 21 1st inverter 2, 22 1st crystal resonator 3, 23 2nd inverter 4, 24 2nd crystal resonator 10, 11 transistor 12-15 diode 16 resistor 17, 317, 417 input node 18, 318, 418 Output node 100, 200 Crystal oscillator circuit 300 Single stage Pierce oscillator 301, 401, 402 Inverter 302, 405 Crystal oscillator 303, 304, 404 Load capacitor 400 Two stage Pierce oscillator 403 Block capacitor

Claims (2)

A first inverter connected between the first voltage line and the second voltage line;
A first crystal resonator having one end connected to the output node of the first inverter;
A second inverter having an input node connected to the other end of the first crystal unit;
And a second crystal resonator having one end connected to an output node of the second inverter and the other end connected to an input node of the first inverter. Each inverter is
A first transistor having a gate connected to an input node, a source connected to the first voltage line, and a drain connected to an output node;
A second transistor having a gate connected to the input node, a source connected to the second voltage line, and a drain connected to the output node;
2. The crystal oscillation circuit according to claim 1, further comprising a feedback resistor having one end connected to the input node and the other end connected to the output node.

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