JP5195293B2 - Oscillator circuit - Google Patents

Description

  The present invention relates to an oscillation circuit that oscillates by attaching an oscillator between a pair of external terminals.

  FIG. 5 shows a configuration diagram of an example of a conventional oscillation circuit. In the figure, an oscillation circuit 1 is formed as a semiconductor integrated circuit, and includes an inverter 4 and a feedback resistor 5 having input / output terminals connected between external terminals 2 and 3. A vibrator 6 is externally attached between the external terminals 2 and 3, and both ends of the vibrator 6 are grounded via capacitors 7 and 8. The oscillation signal generated in the oscillation circuit 1 is output from the terminal 9.

Patent Document 1 describes an oscillating circuit including an inverting amplifier configured to be capable of gain adjustment by a control signal and a waveform shaping circuit configured to be capable of gain adjustment at the time of waveform shaping by a control signal. .
JP 2006-319628 A

  In general, the oscillation circuit 1 to which the vibrator 6 such as a crystal is externally attached is set to an optimum gain according to the vibrator 6 in order to prevent abnormal oscillation and unnecessary radiation noise. On the other hand, even if the oscillation circuit 1 is designed so that the gain is optimized when a crystal is used as the vibrator 6, the ceramic vibrator may be used for reducing the cost or obtaining a desired oscillation frequency depending on the customer. In some cases, a vibrator having a natural frequency different from that of quartz or the like is connected and used as the vibrator 6.

  In such a case, since the gain of the oscillation circuit 1 is not optimized for the ceramic resonator, there is a problem that an oscillation failure such as a decrease in the amplitude level of the oscillation signal occurs.

  The present invention has been made in view of the above points, and provides an oscillation circuit capable of automatically selecting an optimum gain according to an externally attached vibrator and suppressing oscillation failure. Objective.

An oscillation circuit according to an embodiment of the present invention is a semiconductor integrated oscillation circuit that oscillates by externally attaching a vibrator (16) between a pair of external terminals,
An oscillation circuit section (12) having an inverting amplifier (21 to 25) and a feedback resistor (20) connected between the pair of external terminals and outputting an oscillation signal by varying a gain of the inverting amplifier;
An amplitude monitor unit (13) for detecting the amplitude of the oscillation signal output from the oscillation circuit unit and generating a control signal for controlling the gain of the inverting amplifier;
The amplitude monitor unit controls the gain of the inverting amplifier to an optimum gain according to the vibrator externally attached between the pair of external terminals ,
The oscillation circuit unit includes a plurality of inverting amplifiers having different gains, and selects and operates an inverting amplifier according to the control signal,
Furthermore, the amplitude monitor unit includes a plurality of Schmitt circuits (26 to 29) having different hysteresis, and detects the amplitude of the oscillation signal from the rectangular wave signals output from the plurality of Schmitt circuits .

  Preferably, the oscillation circuit unit (12) includes a plurality of inverting amplifiers (21 to 25) having different gains, and selects and operates the inverting amplifier according to the control signal.

  Preferably, the amplitude monitor unit (13) includes a plurality of Schmitt circuits (26 to 29) having different hysteresis, and the oscillation signal is generated from a rectangular wave signal output from the plurality of Schmitt circuits (26 to 29). Detect the amplitude of.

  Preferably, the amplitude monitor unit (13) stops the operation of the plurality of Schmitt circuits (26 to 29) after holding the generated control signal.

  Note that the reference numerals in the parentheses are given for ease of understanding, are merely examples, and are not limited to the illustrated modes.

  According to the present invention, it is possible to automatically select an optimum gain according to an externally attached vibrator, and to suppress an oscillation failure.

<Configuration of oscillation circuit>
FIG. 1 is a block configuration diagram of an embodiment of the oscillation circuit of the present invention, and FIG. 2 is a circuit configuration diagram of an embodiment of the oscillation circuit of the present invention. In both figures, an oscillation circuit section 12 and an amplitude monitor section 13 are provided in the semiconductor integrated circuit 11. A vibrator 16 is externally connected between the external terminals 14 and 15 of the semiconductor integrated circuit 11, and both ends of the vibrator 16 are grounded via capacitors 17 and 18.

  In FIG. 2, the oscillation circuit unit 12 includes a feedback resistor 20 and NOR circuits 21, 22, 23, 24, and 25. The feedback resistor 20 is connected between the external terminals 14 and 15. Each of the NOR circuits 21, 22, 23, 24 and 25 has an output terminal connected to the external terminal 14 and one input terminal connected to the external terminal 15.

  The gains A1, A2, A3, A4, and A5 of the NOR circuits 21, 22, 23, 24, and 25 are different, and gain A1 <gain A2 <gain A3 <gain A4 <gain A5. That is, the high level voltage output from the NOR circuit 21 <the high level voltage output from the NOR circuit 22 <the high level voltage output from the NOR circuit 23 <the high level voltage output from the NOR circuit 24 <the NOR circuit 25. This is related to the output high level voltage.

  A select signal is supplied from a determination circuit 31 described later to the other input terminal of each of the NOR circuits 21, 22, 23, 24, and 25, and the select signal is 0 for each of the NOR circuits 21, 22, 23, 24, and 25. When it is (low level), the NOR operation is performed, and when the select signal is 1 (high level), the NOR operation is stopped.

  The output terminals of the NOR circuits 21, 22, 23, 24 and 25 are connected in common to the output terminal 19 and the amplitude monitor unit 13. The output terminal 19 is a terminal for outputting an oscillation signal generated by the oscillation circuit 12.

  The amplitude monitor unit 13 includes Schmitt circuits 26, 27, 28, 29 and a determination circuit 31. One input terminal of each of the Schmitt circuits 26, 27, 28, and 29 is connected to the output terminal 19, and an oscillation signal output from the oscillation circuit unit 12 is supplied. A stop signal is supplied to the other input terminal of each of the Schmitt circuits 26, 27, 28, and 29 from a determination circuit 31 to be described later, and each of the Schmitt circuits 26, 27, 28, and 29 operates when the stop signal is at a low level. When the stop signal is at a high level, the operation is stopped and a low level signal is output.

  The Schmitt circuit 26 has a first threshold value Va1 and a second threshold value Va2 (Va1> Va2), and the hysteresis Ha = Va1-Va2. The Schmitt circuit 27 has a first threshold value Vb1 and a second threshold value Vb2 (Vb1> Vb2), and hysteresis Hb = Vb1−Vb2.

  The Schmitt circuit 28 has a first threshold value Vc1 and a second threshold value Vc2 (Vc1> Vc2), and hysteresis Hc = Vc1−Vc2. The Schmitt circuit 29 has a first threshold value Vd1 and a second threshold value Vd2 (Vd1> Vd2), and a hysteresis Hd = Vd1−Vd2.

  The hysteresis of each Schmitt circuit is Ha <Hb <Hc <Hd. When the power supply voltage Vcc of the semiconductor integrated circuit 11 is 2.2 V, for example, Ha = 0.5 v, Hb = 1.0 v, Hc = 1.5v and Hd = 2.0v.

  Therefore, the Schmitt circuit 26 outputs a rectangular wave oscillation signal when the difference between the maximum value and the minimum value of the oscillation signal supplied from the oscillation circuit unit 12 exceeds the hysteresis Ha when the stop signal is at a low level. When the difference is equal to or less than the hysteresis Ha, for example, a constant signal is output at a low level.

  The Schmitt circuit 27 outputs a rectangular wave oscillation signal when the difference between the maximum value and the minimum value of the oscillation signal from the oscillation circuit unit 12 exceeds the hysteresis Hb when the stop signal is at a low level. When the hysteresis is lower than Hb, a constant signal is output at a low level, for example.

  The Schmitt circuit 28 outputs a rectangular wave oscillation signal when the difference between the maximum value and the minimum value of the oscillation signal from the oscillation circuit unit 12 exceeds the hysteresis Hc when the stop signal is at a low level. When the hysteresis is equal to or less than the hysteresis Hc, for example, a constant signal is output at a low level.

  The Schmitt circuit 29 outputs a rectangular wave oscillation signal when the difference between the maximum value and the minimum value of the oscillation signal from the oscillation circuit unit 12 exceeds the hysteresis Hd when the stop signal is at a low level. When the hysteresis is lower than Hd, a constant signal is output at a low level, for example.

  The determination circuit 31 performs rectangular wave detection by integrating the output signals of the Schmitt circuits 26 to 29 and comparing them with a threshold value, and detects 1 (high level) when a rectangular wave is detected, and 0 (low level) when no rectangular wave is detected. Level) is obtained. Then, five systems of select signals are generated according to the four systems of rectangular wave detection results.

  FIG. 3 shows the contents of a table indicating the relationship of five systems of select signals to four systems of rectangular wave detection results. That is, when the rectangular wave detection results of the terminals a to d input from the Schmitt circuits 26 to 29 are “0000”, the terminals e to i are set to “11110”. That is, from the rectangular wave detection result, the gain in the NOR circuit 21 is too small, and the gain A5 of the NOR circuit 25 is optimal, and only the NOR circuit 25 performs the NOR operation.

  When the rectangular wave detection results of the terminals a to d input from the Schmitt circuits 26 to 29 are “1000”, the terminals e to i are set to “11101”. In other words, the gain of the NOR circuit 21 is too small from the detection result of the rectangular wave, and the gain A4 of the NOR circuit 24 is optimal, and only the NOR circuit 24 performs the NOR operation.

  When the rectangular wave detection results of the terminals a to d input from the Schmitt circuits 26 to 29 are “1100”, the terminals e to i are set to “11011”. That is, from the rectangular wave detection result, the NOR circuit 21 has a slightly smaller gain, and the NOR circuit 23 has the optimum gain A3, and only the NOR circuit 23 performs the NOR operation.

  When the rectangular wave detection results of the terminals a to d input from the Schmitt circuits 26 to 29 are “1110”, the terminals e to i are set to “10111”. That is, from the rectangular wave detection result, the NOR circuit 21 has a slightly small gain, and the NOR circuit 22 has the optimum gain A2, and only the NOR circuit 22 performs the NOR operation.

  When the rectangular wave detection results of the terminals a to d input from the Schmitt circuits 26 to 29 are “1111”, the terminals e to i are set to “01111”. That is, the gain A1 of the NOR circuit 21 is optimal from the rectangular wave detection result, and only the NOR circuit 21 performs the NOR operation.

  FIG. 4 shows an operation sequence of an embodiment of the operation executed by the determination circuit 31. This operation is started when the semiconductor integrated circuit 11 is powered on.

  In the figure, the decision circuit 31 sets the outputs of the terminals e to i to “01111” in step S 1, supplies a select signal of 0 (low level) only to the NOR circuit 21, and supplies it to the other NOR circuits 22, 23, 24. A 1 (high level) select signal is supplied. Further, each of the Schmitt circuits 26 to 29 is operated by supplying a stop signal of 0 (low level). As a result, the oscillation circuit unit 12 using the NOR circuit 21 as an inverting amplifier starts oscillation using the feedback resistor 20 and the vibrator 16.

  Next, in step S2, the determination circuit 31 generates five systems of select signals using the table shown in FIG. 3, and supplies them to the NOR circuits 21 to 25 from the terminals e to i. As a result, one of the NOR circuits 21 to 25 having an optimum gain for the externally attached vibrator 16 performs a NOR operation. Then, the oscillation circuit unit 12 using one selected NOR circuit having the optimum gain as an inverting amplifier starts oscillation using the feedback resistor 20 and the vibrator 16.

  Thereafter, the determination circuit 31 supplies a 1 (high level) stop signal to each of the Schmitt circuits 26 to 29 in step S3. As a result, the Schmitt circuits 26 to 29 can stop operating and reduce power consumption. The determination circuit 31 holds the five systems of select signals generated in step S2 until the power is cut off, and continues to supply them to the NOR circuits 21 to 25 from the terminals e to i.

  In this way, the optimum gain according to the externally attached vibrator 16 can be automatically selected, and oscillation failure can be suppressed.

It is a block block diagram of one Embodiment of the oscillation circuit of this invention. It is a circuit block diagram of one Embodiment of the oscillation circuit of this invention. It is a figure which shows the content of the table which shows the relationship of the select signal of 5 systems with respect to the rectangular wave detection result of 4 systems. It is a figure which shows the operation | movement sequence of one Embodiment of the operation | movement which a determination circuit performs. It is a block diagram of an example of the conventional oscillation circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Semiconductor integrated circuit 12 Oscillator circuit part 13 Amplitude monitor part 14,15 External terminal 16 Vibrator 17,18 Capacitor 19 Output terminal 20 Feedback resistance 21,22,23,24,25 NOR circuit 26,27,28,29 Schmidt circuit 31 judgment circuit

Claims (2)

A semiconductor integrated oscillation circuit that oscillates with an external oscillator connected between a pair of external terminals,
An oscillation circuit unit having an inverting amplifier connected between the pair of external terminals and a feedback resistor, and changing the gain of the inverting amplifier to output an oscillation signal;
An amplitude monitor unit that detects an amplitude of an oscillation signal output from the oscillation circuit unit and generates a control signal for controlling a gain of the inverting amplifier;
Have
The amplitude monitor unit controls the gain of the inverting amplifier to an optimum gain according to the vibrator externally attached between the pair of external terminals ,
The oscillation circuit unit includes a plurality of inverting amplifiers having different gains, and selects and operates an inverting amplifier according to the control signal,
Furthermore, the amplitude monitor unit includes a plurality of Schmitt circuits having different hysteresis, and detects the amplitude of the oscillation signal from rectangular wave signals output from the plurality of Schmitt circuits. The oscillation circuit according to claim 1 ,
The amplitude monitor unit holds the generated control signal and then stops the operations of the plurality of Schmitt circuits.

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