JP3596282B2 - Crystal oscillation circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a crystal oscillation circuit.
[0002]
[Prior art]
2. Description of the Related Art In recent years, a crystal oscillation circuit has been frequently used as a means for operating a relatively low voltage in a portable electronic device and generating a stable reference frequency with respect to temperature fluctuation.
[0003]
FIG. 5 is a circuit diagram showing an example of a conventional crystal oscillation circuit. In FIG. 5, 31 is a crystal oscillator, 59 is a Colpitts-type crystal oscillation circuit, 58 is a cascode-connected grounded base amplifier, and 57 is a constant voltage circuit.
[0004]
In the conventional crystal oscillation circuit, a cascode-connected grounded base amplifier 58 is connected to the output of a Colpitts-type crystal oscillation circuit 59 using the crystal resonator 31. A constant voltage source VREF is provided at the base of the transistor 49 in order to cancel the temperature change of the base-emitter voltage (hereinafter, referred to as Vbe of the transistor 52) of the transistor 52 in the Colpitts-type crystal oscillation circuit 59 and to maintain the voltage constant. , And applies a fixed voltage to the base of the transistor 52 by dividing the emitter voltage of the transistor 49 by resistance.
[0005]
The operation of the above crystal oscillation circuit will be described below.
[0006]
When the power supply voltage VCC is applied, a fixed voltage that is stable with respect to temperature is generated in the voltage source VREF in the constant voltage circuit 57 in the Colpitts crystal oscillation circuit 59. This fixed voltage is divided by the resistors 23, 24 and 25, and the divided voltage is applied to the base of the transistor 52. If the division ratio at this time is α, a voltage α times the fixed voltage is applied. Here, assuming that a forward voltage generated between the base and the emitter of the transistors 52 and 49 is Vbe, a voltage VE generated at the emitter of the transistor 52 is
VE = αVREF + (α−1) Vbe. Here, α is a value between 0 and 1. To eliminate the influence of Vbe from the emitter voltage VE, α needs to be 1.0.
[0007]
On the other hand, the amplitude taken out by the load resistor 44 is represented by R43 as the value of the resistor 43, R44 as the value of the resistor 44, and VOUT as the output amplitude.
VOUT = (VE / R43) × R44.
[0008]
A current equal to the current value of the constant current source 56 is supplied to the transistor 49. In a normal operating temperature range of −30 ° C. to 80 ° C., the current I3 flowing through the transistor 52 in the Colpitts crystal oscillation circuit 59 and the constant voltage The current I4 flowing through the transistor 49 having the temperature characteristic of Vbe in the circuit 57 is not equal. Therefore, even if it is set to be offset by α to some extent, since an error occurs in Vbe of each transistor, a temperature characteristic occurs in the emitter voltage. When an error occurs in the current, the error in the output voltage is obtained by calculating the current flowing through the transistor 49 as I 4 , the current flowing through the transistor 52 as I 3, the absolute temperature as T, k as the Boltzmann constant, and q as the charge of one electron. , IS as the saturation current of the transistor and the emitter voltage due to the relative error between the currents I3 and I4 as ΔVE, the output amplitude variation ΔVOUT affected by this relative error is:
.DELTA.VOUT = with (ΔVE / R43) × R44 = temperature characteristics of [(α-1) × ( kT / q) × ln {(I 4-I 3) / IS}] × (R4 4 / R4 3) The voltage amplitude will be output.
[0009]
[Problems to be solved by the invention]
As described above, when the conventional Colpitts-type crystal oscillation circuit is used, the temperature change causes the emitter terminal of the transistor 52 to:
Relationship of VE = α VREF + (α- 1) × (kT / q) × ln {(I 4-I 3) / IS}. In addition, since the resistors 44 and 43 also have variations in temperature characteristics, there is a problem that the output amplitude has temperature characteristics.
[0010]
An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a crystal oscillation circuit that outputs a stable oscillation output voltage and amplitude even when the temperature changes, and suppresses this value variation. I do.
[0011]
[Means for Solving the Problems]
In order to solve this problem, a measure taken in claim 1 of the present invention is a Colpitts in which capacitors are individually connected between the base and the emitter of the first transistor and between the emitter and the AC ground terminal of the first transistor. A crystal oscillator circuit, a first resistor having one end connected to the AC ground terminal and the other end connected to the base of the first transistor, a second resistor connected to the base of the first transistor, and an output. A fixed voltage source that outputs a fixed voltage from a terminal, a voltage generation circuit that adds a forward voltage value generated between the base and the emitter of the transistor to an output voltage value of the fixed voltage source and takes out the voltage, A voltage proportional circuit for extracting a voltage proportional to the output voltage value from an output terminal, wherein the output terminal of the voltage proportional circuit is connected to the other end of the second resistor. With this configuration, the voltage generated between the base and the emitter of the transistor is amplified and further divided and applied to the base of the first transistor. And the voltage value generated at the load resistance can be stabilized with respect to the temperature.
[0012]
Next, the means according to claim 2 of the present invention further comprises: a connection row of a crystal unit and a capacitor inserted and connected between the base of the first transistor and the AC ground terminal; And a load connected to the collector, a second transistor for extracting a signal voltage from the collector, and a second resistor inserted between the bases of the first and second transistors. Therefore, the second transistor forms a grounded-base amplifier, and the crystal oscillator is connected between the base of the first transistor and the AC ground terminal. And a stable output signal can be extracted from the resistance of the load.
[0013]
Furthermore, means for claims 3 and 4 was taken of the present invention, electrodeposition ratio example circuit was added to the fixed voltage to generate the base of the transistor, a voltage value proportional to the forward voltage value generated between the emitter It is characterized in that a voltage is taken out from an output terminal.
[0014]
With this configuration, it is possible to amplify only the forward voltage generated between the base and the emitter of the transistor, to facilitate the design of the subsequent resistor division ratio, and to achieve stable oscillation with respect to temperature. The signal output can be easily taken out.
[0015]
Further, a means according to claim 5 of the present invention includes a resistor circuit and a resistor for forming a new resistance value by short-circuiting the Zener diode, and a voltage obtained by dividing a fixed voltage by the resistor circuit and the resistor is provided. The signal is output from an output terminal of the fixed voltage source. Here, the resistance value of this resistance circuit can be adjusted in the adjustment step, and the main voltage and amplitude of the load resistance end with respect to the ambient temperature fluctuation can be adjusted.
[0016]
With this configuration, after the semiconductor integrated circuit is formed, the Zener diode can be short-circuited to change the resistance value, so that the output voltage value can be changed by changing the voltage division ratio.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0022]
FIG. 1 shows a crystal oscillation circuit according to a first embodiment of the present invention. In FIG. 1, a voltage source VREF outputs a substantially constant voltage with respect to a change in temperature. In order to divide and output the voltage of the voltage source VREF, resistors 28 and 29 are connected in series. Is connected to the base of the transistor 3. The other end of the resistor 29 and the collector of the transistor 3 are connected to a ground terminal serving as an AC ground terminal. The emitter of the transistor 3 is connected to the emitter of the diode-connected transistor 4 whose collector and base are connected, and the collector and base of the transistor 4 are connected to the constant current source 53 and the base of the transistor 5 in common. The emitter of the transistor 5 is commonly connected to the emitter of the transistor 6 and the constant current source 55. The collector of the transistor 5 is commonly connected to the collector and the base of the transistor 7 constituting the current mirror circuit and the base of the transistor 8. The emitters of the transistors 7 and 8 are connected to a power supply terminal. The collectors of the transistors 6 and 8 and the base of the transistor 10 are commonly connected, and the base of the transistor 6 is commonly connected to the constant current source 54 and the emitter of the transistor 9. The collector of the transistor 9 is connected to the ground terminal, and the base of the transistor 9 is connected to the connection between the resistors 26 and 27. Here, the other end of the resistor 27 is connected to the ground terminal, and the other end of the resistor 26 is connected to the collector of the transistor 10 and the resistor 25. The emitter of transistor 10 is connected to a power supply terminal. The other end of the resistor 25 is commonly connected to a capacitor 33 for buffering the influence of the oscillation output, the resistor 24 and the base of the transistor 2.
[0023]
The other end of the capacitor 33 is connected to the ground terminal, and one side of the resistor 24 is commonly connected to the crystal oscillator 31 and the resistor 23, the capacitor 34 of the Colpitts oscillation circuit, and the base of the transistor 1. The emitter of the transistor 2 is connected to the collector of the transistor 1, and the collector of the transistor 2 is commonly connected to one end of a capacitor 36 that couples the resistor 22 and the oscillation output and outputs the result. The other end of the resistor 22 is connected to a power terminal.
[0024]
The capacitor 36 is commonly connected to the capacitor 46, which is also the load of the oscillation circuit, the resistor 47, and the output terminal. The other ends of the capacitor 46 and the resistor 47 are connected to a ground terminal. One side of the capacitor 34 is commonly connected to the capacitor 35, the resistor 21 for determining the output current value, and the emitter of the transistor 1. The other ends of the capacitor 35 and the resistor 21 are connected to a ground terminal.
[0025]
One side of the crystal unit 31 is connected to one end of the variable capacitance diode 32 and the resistor 30, and the other end of the variable capacitance diode 32 is connected to the ground. The other end of the resistor 30 is connected to a voltage application terminal VC.
[0026]
The operation of this crystal oscillation circuit will be described below.
[0027]
First, the power supply voltage VCC is applied to the power supply of the circuit. Next, when a reference input voltage with little variation is applied to the input voltage VREF even when the power supply and the temperature fluctuate, the voltage value V1 at the connection between the resistors 28 and 29, the base voltage value V2 of the transistor 9, and the The collector voltage value V3 and the emitter voltage value V4 of the transistor 1 are represented by R23 to R29 for each of the resistors 23 to 29, the current value flowing through the transistor 1 is I3, the current value of the current source 53 is I4, and the saturation current value is IS. , The Boltzmann constant is k, the absolute temperature is T, and the charge amount of electrons is q,
V1 = VREF × R29 / (R28 + R29)
V2 = V1 + (kT / q) × ln (I4 / IS)
V3 = V2 × (R26 + R27) / R27
V4 = V3 × R23 / (R23 + R24 + R25) − (kT / q) × ln (I3 / IS). As a result, when VBE changes due to temperature fluctuation (ΔT), the fluctuation amount β of the base voltage value of the transistor 1 becomes
β = k ｛(ΔT) / q｝ × ln (I4 / IS) × (R26 + R27) / R27 × R23 / (R23 + R24 + R25), where β is the temperature fluctuation and the voltage fluctuation of the emitter of the transistor 1 ｛ k (ΔT) / q ｝ × ln (I3 / IS) is satisfied , and a stable output amplitude is obtained.
[0028]
As described above, according to the present embodiment, a temperature change does not occur in the output amplitude by using an operational amplifier to output a voltage that cancels out the temperature characteristics of the NPN transistor, which is also a cause of the temperature fluctuation of the output terminal. The amplitude can be output. In addition, a stable output amplitude can be obtained by adding a circuit for adjusting a resistance value for decreasing the voltage of VREF.
[0029]
FIG. 2 is a crystal oscillation circuit diagram of a second embodiment in which the resistor 29 of FIG. Since the resistance value of the resistance circuit 60 is adjusted in the adjustment step, it is possible to adjust the output voltage and the amplitude of the load resistance 22 with respect to the ambient temperature fluctuation.
[0030]
FIG. 3 is a diagram showing an embodiment of the resistance circuit 60 of FIG.
[0031]
In FIG. 3A, resistors 61 to 63 are connected in series, and a Zener diode is connected in parallel with the resistors 61 and 62. Pads TP1 to TP3 are connected to terminals of each Zener diode so that voltage or current can be applied. For example, by applying a current between TP1 and TP2 to short-circuit the Zener diode 67, the resistance value between TP1 and TP2 can be set to a new value.
[0032]
FIG. 3B shows a configuration in which the resistor 64 and the Zener diode 69, the resistor 65 and the Zener diode 70, the resistor 66 and the Zener diode 71 are connected in series, and further, each is connected in parallel. For example, a new resistance value can be formed by short-circuiting the Zener diode 69 by applying a current between the TP4 and the ground terminal.
[0033]
The adjustment accuracy of the resistor circuit 60 can be increased by increasing the number of resistors in FIGS. 3A and 3B, and the adjustment accuracy can be made different by making each resistance value different as needed.
[0034]
Figure 4 is a third crystal oscillator circuit diagram that shows an embodiment of the present invention.
[0035]
In the figure, a voltage source VREF outputs a substantially constant voltage with respect to a change in temperature, and resistors 28 and 29 are connected in series to divide and output the voltage of the voltage source VREF. Is connected to the base of the transistor 90. A differential amplifier circuit is formed in which the emitters of the transistors 90 and 91 are commonly connected. A voltage substantially equal to the base voltage of the transistor 90 is output to the collector and base of the transistor 91. The collector and base of the transistor 91 are connected to the emitter of a transistor 92. A resistor 93 is connected between the base and the emitter of the transistor. The current divided by the value of flows. Since the base current of the transistor is small enough to be ignored, a current having the same value as the current flowing through the resistor 93 flows through the resistor 94 connected to the base of the transistor 92. The other end of the resistor 94 is connected to the collector of the transistor 92 and the current source 53, and a constant current is supplied from the current source 53. In the above configuration, a voltage that is the sum of the voltage proportional to the value of the voltage source VREF and the voltage proportional to the forward voltage between the base and the emitter of the transistor is output to the connection between the resistor 94 and the current source 53. Is done. Here, the obtained voltage is applied to a series circuit of resistors 23 to 25 via a voltage driving circuit including transistors 5 to 8 and 10 and a current source 55. The voltage generated at the connection between the resistors 23 and 24 is applied to the base of the transistor 1. In this manner, a voltage which is proportional to the value of the voltage source VREF and is obtained by dividing this value with respect to the voltage proportional to the forward voltage between the base and the emitter of the transistor is applied to the base of the transistor 1. . By adjusting the ratio of the sum of the resistors 24 and 25 and the value of the resistor 23 to the ratio of the values of the resistors 93 and 94, the variation in the voltage applied to the base of the transistor 1 with respect to the temperature can be reduced. It can be adjusted to the temperature fluctuation of the emitter forward voltage value. In this manner, a substantially constant voltage with respect to temperature is output to the emitter voltage of the transistor 1, so that a constant DC voltage with respect to temperature can be taken out to the load resistor 22, and A substantially constant oscillation signal can be extracted.
[0036]
【The invention's effect】
As described above, the present invention reduces the output amplitude fluctuation due to the temperature change and adjusts the resistance value by using the operational amplifier for the temperature characteristic of the output amplitude that cannot be corrected only by the VBE in the crystal oscillation circuit. By employing a configuration in which a circuit is added, an excellent crystal oscillation circuit that can output a stable amplitude can be realized.
[Brief description of the drawings]
FIG. 1 is a crystal oscillation circuit diagram showing a first embodiment of the present invention. FIG. 2 is a crystal oscillation circuit diagram showing a second embodiment of the present invention. FIG. 3 is a diagram showing the resistance circuit of FIG. FIG. 4 is a circuit diagram showing a crystal oscillation circuit according to a third embodiment of the present invention. FIG. 5 is a diagram showing a conventional crystal oscillation circuit.
1 to 10 bipolar transistors 21 to 30 resistor 31 crystal oscillator 32 variable capacitance diode 33 to 36 capacitor 40 to 42 capacitor 43, 44 resistor 45, 46 capacitor 47 resistor 48 to 52 transistor 53 to 56 current source 57 constant voltage circuit 58 base Ground voltage amplifying circuit 59 Colpitts-type crystal oscillation circuit 60 Current adjusting resistance adjusting circuits 61 to 66 Resistance 67 to 71 Zener diode 90 to 92 Transistors 93, 94 Resistance

Claims (5)

A Colpitts-type crystal oscillation circuit in which capacitors are individually connected between the base and the emitter of the first transistor and between the emitter and the AC ground terminal of the first transistor;
A first resistor having one end connected to the AC ground terminal and the other end connected to the base of the first transistor;
A second resistor connected to the base of the first transistor;
A fixed voltage source that outputs a fixed voltage from the output terminal;
A voltage generating circuit that adds a forward voltage value generated between a base and an emitter of the transistor to an output voltage value of the fixed voltage source and takes out the voltage;
A voltage proportional circuit that takes out a voltage proportional to the output voltage value of the voltage generating circuit from an output terminal,
A crystal oscillation circuit in which an output terminal of the voltage proportional circuit is connected to the other end of the second resistor. A Colpitts-type crystal oscillation circuit in which capacitors are individually connected between the base and emitter of the first transistor, between the emitter and the AC ground terminal;
A connection row of a crystal unit and a capacitor inserted and connected between the base of the first transistor and the AC ground terminal;
A second transistor having a collector connected to the emitter of the first transistor, a load connected to the collector, and extracting a signal voltage from the collector;
A first resistor having one end connected to the AC ground terminal and the other end connected to the base of the first transistor;
A second resistor having one end connected to the base of the first transistor and the other end connected to the base of the second transistor;
A fixed voltage source that outputs a fixed voltage from the output terminal;
A voltage generating circuit that adds a forward voltage value generated between a base and an emitter of the transistor to an output voltage value of the fixed voltage source and takes out the voltage;
A voltage proportional circuit that takes out a voltage proportional to the output voltage value of the voltage generating circuit from an output terminal,
A crystal oscillation circuit in which an output terminal of the voltage proportional circuit and the other end of the second resistor are connected. A Colpitts-type crystal oscillation circuit in which capacitors are individually connected between the base and the emitter of the first transistor and between the emitter and the AC ground terminal of the first transistor;
A first resistor having one end connected to the AC ground terminal and the other end connected to the base of the first transistor;
A second resistor connected to the base of the first transistor;
A fixed voltage source that outputs a fixed voltage from the output terminal;
A voltage proportional circuit that generates a voltage value proportional to a forward voltage value generated between the base and the emitter of the transistor and takes out a voltage added to the fixed voltage from an output terminal;
A crystal oscillation circuit in which an output terminal of the voltage proportional circuit is connected to the other end of the second resistor. A Colpitts-type crystal oscillation circuit in which capacitors are individually connected between the base and emitter of the first transistor, between the emitter and the AC ground terminal;
A connection row of a crystal unit and a capacitor inserted and connected between the base of the first transistor and the AC ground terminal;
A second transistor having a collector connected to the emitter of the first transistor, a load connected to the collector, and extracting a signal voltage from the collector;
A first resistor having one end connected to the AC ground terminal and the other end connected to the base of the first transistor;
A second resistor having one end connected to the base of the first transistor and the other end connected to the base of the second transistor;
A fixed voltage source that outputs a fixed voltage from the output terminal;
A voltage proportional circuit that generates a voltage value proportional to a forward voltage value generated between the base and the emitter of the transistor and takes out a voltage added to the fixed voltage from an output terminal;
A crystal oscillation circuit in which an output terminal of the voltage proportional circuit and the other end of the second resistor are connected. 5. The fixed voltage source according to claim 1, wherein a voltage obtained by dividing a fixed voltage by a resistor and a resistor that forms a new resistance value by short-circuiting the Zener diode is output from an output terminal of the fixed voltage source. Crystal oscillation circuit.

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