JP2022063159A - Oscillation circuit for OCXO - Google Patents

Abstract

To provide an oscillation circuit having small clock frequency deviation with respect to changes in an environmental temperature.SOLUTION: The present invention provides an oscillation circuit for an OCXO which includes: a temperature sensor generating an output voltage that is a linear function of a temperature; a non-inverting amplifier and an inverting amplifier to which the output of the temperature sensor is input; an MOS transistor having a gate to which the output of the non-inverting amplifier is input; an MOS transistor having a gate to which the output of the inverting amplifier is input; a resistance to which the sum of drain currents of the two MOS transistors flow; a constant voltage source connected to the sources of the two MOS transistors; a buffer amplifier circuit for the voltage of the resistance; and a VCXO using the output of the buffer amplifier circuit as a control voltage. The oscillation circuit for an OCXO is characterized in that the sum of the drain currents is adjusted to have approximate secondary characteristics of the temperature by a constant voltage source connected to the sources of the MOS transistors.SELECTED DRAWING: Figure 1

Description

The present invention is a temperature compensation circuit for OCXO (Oven Controlled Crystal Oscillator) that generates a stable reference clock signal with a frequency required for a fifth generation communication system (called 5G). Regarding.

With the recent increase in communication speed and sophistication of communication technology, the standards regarding the frequency stability of the communication reference clock are becoming stricter every day. The frequency stability standard for changes in environmental temperature is one of them. Therefore, OCXO (Oven Controlled Crystal Oscillator), which operates an AT-cut oscillator or SC-cut oscillator in a constant temperature bath, has been used in order to obtain a clock signal whose frequency fluctuation is extremely small with respect to changes in environmental temperature. .. In OCXO, the frequency of the clock signal, which is the output of the oscillator, is set by setting the temperature of the constant temperature bath to the temperature at which the frequency temperature characteristic (frequency deviation) of the oscillator becomes zero (this is called the zero temperature special temperature). It is also described as the oscillation frequency.) To stabilize it. In recent years, there has been an increasing demand for miniaturization of OCXO, and it has become difficult to keep the temperature inside the miniaturized constant temperature bath accurately and constant with respect to temperature changes in the external environment. In order to obtain an extremely stable frequency signal even if there is a slight temperature change in the constant temperature bath, it is necessary to incorporate a temperature compensation circuit into the oscillation circuit that cancels the fluctuation of the oscillation frequency due to the temperature fluctuation of the constant temperature bath. Conventionally, a so-called TCXO (Temperature Compensated Crystal Oscillator) has been used as a temperature compensating oscillator for this purpose, but the TCXO has been developed for the purpose of temperature compensating for a wide range of temperature changes (for example, Patent Documents). 1) It is not suitable for OCXOs that perform accurate temperature correction under extremely small temperature changes.

JP-A-2011-023944

FIG. 5A is a diagram showing the temperature characteristics of the oscillation frequency deviation at a temperature near the zero temperature special temperature (here, 90 ° C.) of the crystal oscillator. Even if the frequency deviation is set to zero (0) at the zero temperature special temperature, the frequency deviation is about 80 ppb when the frequency deviation is 2 ° C. from the zero temperature special temperature (90 ° C.), and the frequency deviation is about 500 ppb when the frequency deviation is 5 ° C. This means that even if the set temperature of the constant temperature bath can be adjusted to the zero temperature special temperature of the oscillator, the temperature inside the OCXO package will be, for example, 2 for a wide environmental temperature change from -40 ° C to 80 ° C. It means that a frequency deviation of 80 ppb occurs when the temperature fluctuates. It also means that if there is an error in matching the set temperature of the constant temperature bath and the zero temperature special temperature of the oscillator, a larger frequency deviation will occur. For an oscillator used for high-speed communication of 5G or later, it is necessary to accurately adjust the temperature of the constant temperature bath to the zero temperature special temperature (here, 90 ° C.) of the oscillator. This temperature adjustment has become a big problem in mass production. Furthermore, due to recent demands for miniaturization of OCXO packages, it has become extremely difficult to keep the temperature inside the package constant against a wide change in environmental temperature from -40 ° C to 80 ° C. Against this background, there is an increasing demand for OCXO temperature compensation circuits that realize a clock signal frequency deviation of 20 ppb or less, preferably 10 ppb or less within a temperature range of ± 5 ° C. from the zero temperature special temperature.

The AT-cut oscillator and the SC-cut oscillator show frequency fluctuation characteristics proportional to the square of the temperature fluctuation width at the temperature near the zero temperature special temperature change point. The present invention provides an oscillation circuit having a frequency compensation circuit proportional to the square of the temperature fluctuation. That is, it is an oscillator circuit for OCXO having a temperature compensation circuit, and specifically, it has the following features.
(1) In the present invention, a temperature sensor that generates an output voltage that is a linear function of temperature, a non-inverting amplifier and an inverting amplifier that input the output of the temperature sensor, and a MOS in which the output of the non-inverting amplifier is input to the gate. A transistor, a MOS transistor in which the output of the inverting amplifier is input to the gate, a resistor in which the sum of the drain currents of the two MOS transistors flows in, a buffer amplifier circuit that receives the voltage of the resistor generated by the current, and the buffer amplifier circuit. It is an oscillator circuit for OCXO (crystal oscillator with a constant temperature bath) characterized by including VCXO (voltage control crystal oscillator) which used the output of (voltage control) as a control voltage.

(2) In addition to (1), the present invention has the same input voltage and output voltage of the non-inverting amplifier at zero temperature special temperature (temperature at which the frequency deviation becomes zero), and also with the input voltage of the inverting amplifier. The output voltage is also the same, and the temperature characteristic straight line of the output voltage of the non-inverting amplifier and the temperature characteristic straight line of the output voltage of the inverting amplifier intersect at the zero temperature special temperature, and the amplification factors of the non-inverting amplifier and the inverting amplifier are high. It is characterized by being variable.

(3) In addition to (1) and / or (2), the present invention is a constant voltage source for adjusting the source voltage of the MOS transistor so that the sum of the drain currents has a secondary characteristic of the temperature. The control voltage of the VCXO is generated from the sum of the voltage of the resistor and the voltage from the constant voltage source connected in series with the resistor. , Or both, and the two MOS transistors are characterized by having the same drain current characteristics of the MOS.

In the temperature compensation circuit used in the OCXO oscillation circuit of the present invention, the parameters of the frequency correction circuit can be adjusted according to the frequency temperature characteristics of the individual crystal oscillation circuits, so that the corrected clock frequency deviation is extremely reduced to 10 ppb to 20 ppb or less. It can be made smaller. In particular, AT-cut oscillators and SC-cut oscillators show frequency fluctuations proportional to the square of temperature fluctuations in the vicinity of the zero temperature special temperature, but the drain current in the saturation region of the MOS transistor is the relationship between the gate-source voltage and the square. Since the temperature compensation circuit of the present invention utilizing the above shows a very good match with the temperature characteristic of the frequency deviation of the crystal oscillator, the matching error can be made very small by a simple circuit. As a result, it is possible to provide an oscillator having an extremely small frequency deviation even in high-speed communication in recent years.

FIG. 1 is a diagram showing an example of the frequency correction temperature compensation circuit of the present invention, and is a temperature compensation circuit for OCXO using the VG-ID (gate-source voltage-drain current) characteristic of the polyclonal transistor. FIG. 2 is a diagram showing a second embodiment of the present invention, and is a temperature compensation circuit for OCXO that utilizes the VG-ID (gate-source voltage-drain current) characteristic of the NOTE transistor. FIG. 3 is a diagram showing a frequency variable characteristic of the VCXO. FIG. 4 is a diagram showing temperature characteristics of voltage and current at the main terminals shown in the temperature compensation circuit of FIG. FIG. 5 is a diagram illustrating a method of reducing the frequency deviation of the clock signal in the present invention. FIG. 6 is a diagram showing a frequency deviation (matching error) when the source voltage VE of the MIMO transistor in the temperature compensation circuit of _FIG . 1 changes. FIG. 7 is a diagram showing an oscillator circuit for OCXO having the temperature compensation circuit of the present invention. FIG. 8 is a diagram showing the frequency temperature characteristics of the crystal unit.

An object of the present invention is to provide an oscillation circuit that generates a clock signal with a small change in frequency temperature. FIG. 8 is a diagram showing the frequency temperature characteristics of the AT-cut and SC-cut crystal oscillator circuits without temperature compensation. The horizontal axis shows the temperature, and the vertical axis shows the amount of frequency change (frequency deviation Δf / f). In FIG. 8A, what is shown by a group of six cubic curves is the frequency temperature characteristic of the AT-cut crystal oscillator, and the cutting angle of the crystal is used as a parameter. The temperature characteristic of the AT-cut type oscillator is a cubic curve as shown in FIG. 8, but the curve having a zero temperature special temperature near 90 ° C. is a substantially quadratic curve of the temperature near the temperature. The upwardly convex curve having a zero temperature special temperature near 90 ° C. is the frequency temperature characteristic of the SC cut crystal oscillator, which is also a quadratic curve of the temperature. As can be seen from FIG. 8A, the temperature characteristic of the AT-cut type oscillator has the smallest frequency change with respect to temperature fluctuation in the vicinity of the temperature showing the maximum or minimum. Further, regarding the temperature characteristics of the SC cut type oscillator, the frequency change with respect to the temperature fluctuation is the smallest in the vicinity of the temperature showing the maximum. By using the crystal oscillator in this way before and after the temperature indicating the maximum or minimum, the frequency change with respect to the temperature change can be reduced.

For example, as shown in FIG. 8B, an AT-cut type oscillator in which the temperature at which the minimum value is 90 ° C. and the frequency change amount (Δf / f) at that time is zero, or the temperature at which the maximum value is reached. If the crystal oscillator is operated at around 90 ° C. using an SC cut type oscillator whose frequency is 90 ° C. and the frequency change amount (Δf / f) at that time is zero, the frequency change amount (Δf / f) ) Can be created as a small oscillator. The OCXO oscillator utilizes this feature.

However, in the age of 5G, there is an increasing demand for miniaturization of OCXO. When the OCXO is miniaturized, it is difficult to keep the temperature inside the package constant against external temperature changes, and assuming that the temperature change inside the OCXO is, for example, 90 ° C ± 2 ° C, as described above. The frequency is forced to change by about 80 ppb. However, in 5G high-speed communication, the oscillation circuit that generates the reference clock is required to operate stably with a very small frequency change (for example, 20 ppb or less, preferably 10 ppb or less). The present invention provides an OCXO oscillator that achieves a frequency temperature change of 10 ppb or less.

FIG. 7 is a diagram showing an oscillator circuit for OCXO having the temperature compensation circuit of the present invention. In the constant temperature bath (OVEN) package, there are a temperature compensation circuit, a VCXO (voltage controlled crystal oscillator) that uses the output voltage of the temperature compensation circuit as the control voltage Vc, and a heat source (Heater) that keeps the crystal oscillator at a predetermined temperature. A heat source control IC (Heater Control IC) is housed, and a clock signal is output from the VCXO circuit. In this figure, the VCXO circuit is composed of two inverters, a feedback resistor Rf, a limiting resistor Rd, a capacitor Cc, Cpg, Cpd, a bias resistor Rv, a varicap, etc., and the control voltage Vc of the VCXO circuit is temperature compensated. It is supplied from the circuit (Temperature Compensation Circuit). These VCXO circuits and temperature compensation circuits are incorporated in one IC (oscillation IC: OSC IC). The present invention is an OCXO circuit having such a temperature compensation circuit.

FIG. 1 is a diagram showing an example of a frequency correction temperature compensation circuit of the present invention that reduces the frequency deviation of the crystal oscillator circuit to 10 ppb or less. This is a temperature compensation circuit for OCXO that utilizes the VG-ID (gate-source voltage-drain current) characteristics of a polyclonal transistor. The circuit shown in FIG. 1 is an arithmetic amplifier circuit, V ( BTR) A non-inverting amplifier consisting of an OP amplifier 28 and an inverting amplifier consisting of an OP amplifier 27 that input voltage, a PMOS transistor 31 in which the BT output of the OP amplifier 28 is input to the gate, and a BTA output of the OP amplifier 27 input to the gate. PMOS transistor 33, a constant voltage source 32 connected to the source of these two PMOS transistors 31, 33, and a series of resistors 35 and a resistor 35 into which the sum of the drain currents of these two PMOS transistors 31, 33 flows. It is composed of a connected constant voltage source 34, a buffer amplifier circuit 36 to which a sum VTO of the voltage of the resistor 35 and the constant voltage source 34 is input, and / or an inverting amplifier 41. The output V (VT) of the buffer amplifier circuit 36 or the output Vc of the inverting amplifier 41 is used as the control voltage of the VCXO (voltage controlled crystal oscillator). FIG. 3 is a diagram showing the frequency variable characteristics of the VCXO, in which the control voltage is shown on the horizontal axis and the frequency deviation is shown on the vertical axis. The oscillation frequency of the VCXO has a characteristic that it changes linearly with respect to the control voltage as shown in FIG. On the other hand, under a constant control voltage, the oscillation frequency of the VCXO has a secondary characteristic with respect to the temperature near its zero temperature special temperature. Therefore, in order to cancel the temperature change at that frequency, the control voltage Vc or V ( VT) must be a quadratic function of temperature. Hereinafter, it will be explained sequentially that Vc and V (VT) are quadratic functions of temperature, and that the oscillation frequency of OCXO using these voltages as a control voltage can be suppressed to a fluctuation of 10 ppb or less with respect to a temperature change. do.

The temperature sensor 11 used in the temperature compensation circuit of the present invention outputs a voltage that is a linear function of temperature. Such a temperature sensor can be easily manufactured from, for example, a bandgap reference circuit. The temperature sensor output Vtemp is input to a non-inverting amplifier composed of an OP amplifier 14, resistors 13, 15 and a constant voltage source 12 in order to increase the temperature sensitivity and secure the drive capability for the subsequent circuit. The voltage V (BTO) in which the temperature sensor output Vtemp is amplified is output to the output terminal BTO of the non-inverting amplifier. In this circuit, the temperature sensor outputs Vtemp and V (BTO) are assumed to be grounded reference voltages. In order to convert V (BTO) from the ground reference voltage to the power supply reference voltage, it is connected to a voltage reference conversion circuit consisting of an inverting amplifier 19 and resistors 16, 17, 18 and 21. That is, the voltage reference conversion circuit outputs VDD—V (BTO) voltage V (BTR) from the output terminal BTR. The voltage V (BTR) is input to the non-inverting amplifier 28 and the inverting amplifier 27 in the next stage. It should be noted that the part up to the part that outputs V (BTO) or V (BTR) can be considered as a temperature sensor circuit.

When V (BTR) is input to the non-inverting amplifier consisting of the OP amplifier 28, the constant voltage source 22 (voltage Vr1), and the resistors 23 and 24, if there is no offset voltage of the OP amplifier 28, the output voltage V (BT) < Voltage at output terminal BT>
V (BT) = (1 + R2 / R1) (V (BTR) -Vr1) + Vr1
Will be. As described above, the output voltage V (BT) of the non-inverting amplifier can be adjusted by the constant voltage source 22 (voltage Vr1) and the resistors R1 and R2, and the amplification factor can also be changed. In the temperature compensation circuit of the present invention, the output voltage V (BT) of the non-inverting amplifier is equal to the input voltage V (BTR) of the crystal oscillator at the zero temperature special temperature (temperature at which the frequency deviation becomes zero, for example, 90 ° C.). Adjust Vr1 so that it becomes (same as adjusting Vr1 to V (BTR)). By doing so, it is possible to prevent the V (BT) value of the zero temperature special temperature from fluctuating when the amplification factor is adjusted by R1 or R2, and it is easy to adjust the temperature compensation for variations in the temperature characteristics of individual crystal oscillators. become.

When V (BTR) is input to the inverting amplifier consisting of the OP amplifier 27 and the constant voltage source 26 (voltage Vr2) resistors 25 and 29, if there is no offset voltage of the OP amplifier 27, the output voltage V (BTA) <output terminal Voltage in BTA>
V (BTA) =-(R4 / R3) (V (BTR) -Vr2) + Vr2
Will be. In this way, the output voltage V (BTA) of the inverting amplifier can be adjusted by the constant voltage source 26 (voltage Vr2) and the resistors R3 and R4, and the amplification factor can also be changed. In the temperature compensation circuit of the present invention, Vr2 so that the output voltage V (BTA) of the inverting amplifier becomes equal to the input voltage V (BTR) at the zero temperature special temperature (temperature at which the frequency deviation becomes zero, for example, 90 ° C.). (Same as adjusting Vr2 to V (BTR)). As a result, the value of V (BTA) of the zero temperature special temperature of the crystal oscillator can be made constant with respect to the adjustment of the amplification factor by R3 or R4, so that the temperature correction sensitivity can be easily adjusted with respect to the temperature characteristics of the crystal oscillator. .. If the offset voltage of both the OP amplifier 28 and the OP amplifier 27 is zero,
V (BTR) = V (BT) = Vr1 = V (BTA) = Vr2
However, since the OP amplifier 28 and the OP amplifier 27 generally have different offset voltages, it is necessary to separately prepare the constant voltage source 22 of Vr1 and the constant voltage source 26 of Vr2.

The output V (BT) of the non-inverting amplifier is input to the gate of the MIMO transistor 31 and controls the drain current ia1 of the MIMO transistor 31. Further, a back gate voltage ( _VE ) is applied to the source side of the MIMO transistor 31 by the constant voltage source 32, and the operating region of the drain current is determined. If the MIMO transistor 31 can be operated in the saturation region by adjusting VE, the drain (saturation) current _ia1 can be determined from the gate voltage (gate-source voltage Vgs) and the threshold voltage (Vtp) of the MIMO transistor.
ia1 ≒ K (Vgs-Vtp) ²
(K is a constant of proportionality, so-called K value). Here, since the gate voltage (Vgs) is V (BT) _-VE and is a linear function of temperature, the drain current ia1 is a quadratic function of temperature (when Vgs-Vtp> 0).

Similarly, the output V (BTA) of the inverting amplifier 27 is input to the gate of the MIMO transistor 33 to control the drain current ia2 of the MIMO transistor 33. Further, a back gate voltage ( _VE ) is applied to the source side of the MIMO transistor 33 by the constant voltage source 32, and the operating region of the drain current is determined. If the MIMO transistor 33 can be operated in the saturation region by adjusting VE, the drain (saturation) current _ia2 can be determined from the gate voltage (gate-source voltage Vgs) and the threshold voltage (Vtp) of the MIMO transistor.
ia2 ≒ K (Vgs-Vtp) ²
Will be. Here, since the gate voltage (Vgs) is V (BTA) _-VE and is a linear function of temperature, the drain current ia2 is a quadratic function of temperature (when Vgs-Vtp> 0). .. If it is desired to correct the difference between the threshold values of the MIMO transistors 31 and 33, different _VE voltages may be applied to the sources of the respective MIMO transistors by different constant voltage sources.

FIG. 4A shows the temperature characteristics of the voltages of Vtemp, V (BTR), V (BT), and V (BTA) described above. Here, FIG. 4 is a diagram showing the temperature characteristics of voltage and current at the main terminals shown in the temperature compensation circuit of FIG. Both V (BT) and V (BTA) are output voltages that are linear functions of temperature, and the slopes that intersect at the zero temperature special temperature are straight lines that are opposite to each other (symmetric with respect to the voltage at the zero temperature special temperature). It has a relationship). When the voltage of V _E is adjusted, ia1 hardly flows at a temperature lower than the zero temperature special temperature, but the current ia2 flows, and at a temperature higher than the zero temperature special temperature, ia2 hardly flows and the current ia1 flows. Become. Therefore, the sum of the drain (saturation) currents (ia1 + ia2) of the two MIMO transistors 31 and 33 is approximately a quadratic function (quadratic characteristic) of the temperature. This situation is shown in FIG. 4 (b). Here, <about> is a slight deviation from the strict quadratic function because, for example, in an actual MOS transistor, the drain (saturation) current does not completely become zero in the subthreshold region (region below the threshold voltage). Means that By adjusting the current values of _ia1 and ia2 at the zero temperature special temperature with VE, the sum of the currents (ia1 + ia2) can be brought closer to the secondary characteristic of the temperature.

The drain (saturation) currents of the two MIMO transistors 31 and 33 merge at the terminal VTO and flow to the constant voltage source 34 (voltage Voff) via the resistor 35. The voltage V (VTO) of the terminal VTO is the sum of the voltage Voff and the voltage applied to the resistance 35. Since the voltage applied to the resistor 35 is proportional to the sum of the drain (saturation) currents (ia1 + ia2), the voltage V (VTO) also has a secondary characteristic with respect to temperature. When this voltage V (VTO) is input to the voltage follower (buffer amplifier) circuit of the OP amplifier 36, it is output from the terminal VT (output voltage V (VT) = V (VTO)), and the OP amplifier 41 has a constant voltage. It is inverted by an inverting amplifier consisting of a source 39 and resistors 37 and 38, and is output from the terminal VC (output voltage Vc). The temperature characteristics of the output voltages V (VT) and Vc are shown in FIG. 4 (c). When the VCXO has the frequency variable characteristics as shown in FIG. 3 with respect to the control voltage input, the frequency temperature characteristics of the output voltage V (VT) are convex upward (the frequency is the maximum value at the zero temperature special temperature). Used for frequency correction of crystal oscillators such as SC cut, the output voltage Vc is a crystal oscillator such as AT cut whose frequency temperature characteristic is convex downward (the frequency is the minimum value at zero temperature special temperature). If it is used for frequency correction, the temperature characteristics of the oscillation frequency can be reduced. The Voff voltage and the VI voltage of the constant voltage source 39 serve as the bias voltage of the OP amplifier 36 and the OP amplifier 41, and also adjust the frequency of the oscillation circuit at the zero temperature special temperature (this adjustment is for fine adjustment). It also plays the role of.).

FIG. 5 shows the temperature characteristics of the oscillation frequency (clock frequency) of the oscillator using the AT crystal oscillator as shown in FIG. 8B, using the output voltage Vc of the temperature compensation circuit described in FIG. 4 to obtain the temperature of the oscillation frequency. An example of compensation is shown. The procedure is shown in Steps 1 to 3 below.
Step1 Set OCXO to zero temperature special temperature (90 ° C) and adjust Voff voltage or VI voltage to set the oscillation frequency to the target value. (Fig. 5 (a) is a graph based on the frequency deviation after this frequency adjustment.)
Step2 Set the temperature of the OCXO oscillator circuit to 85 ° C, change the Vc of the gain of the inverting amplifier of the OP amplifier 27 by adjusting the resistor 29 or the resistor 25, and set the oscillation frequency to the target value (the set value at the zero temperature special temperature). Match so that it becomes the same). If the above-mentioned Vr2 is adjusted, this adjustment does not involve a change in Vc at the zero temperature special temperature, and therefore does not affect the oscillation frequency at the zero temperature special temperature in Step 1.
Step3 Set the temperature of the OCXO oscillation circuit to 94.5 ° C, change the Vc by adjusting the gain of the non-inverting amplifier of the OP amplifier 28 by adjusting the resistor 24 or the resistor 23, and set the oscillation frequency to the target value (at zero temperature special temperature). (Set value of). This adjustment does not affect the oscillation frequency at the zero temperature special temperature in Step 1 as long as the above-mentioned Vr1 is adjusted.

FIG. 5B shows the temperature characteristics of the frequency correction amount by the circuit after the combination of Step 2 and Step 3. FIG. 5 (c) is a diagram in which FIGS. 5 (a) and 5 (b) are drawn on the same graph. These two characteristics almost overlap, but there is a slight difference. The reason is that the frequency characteristic of the AT crystal oscillator, which is originally the third-order characteristic of temperature, is corrected by the quadratic function of temperature, and the temperature correction characteristic is completely using the drain current characteristic of the MOS transistor. This is because it is not a quadratic function. FIG. 5D is an enlarged view of the difference between the frequency temperature characteristic of the crystal oscillator and the temperature correction characteristic of the correction circuit, and shows the frequency temperature characteristic after frequency correction. The curve shown by <matching> with frequency tuning at 85 ° C, 90 ° C, and 94.5 ° C shows the frequency deviation of 500 ppb before frequency correction when the temperature inside the OCXO was between 85 ° C and 95 ° C (Fig.). It is shown that 5 (a)) is suppressed to 5 ppb or less after frequency correction. Needless to say, if the temperature of the frequency adjustment in STEP 2 and STEP 3 is brought close to 90 ° C., the frequency deviation in the vicinity of the temperature range can be further reduced.

FIG. 6 is a diagram showing a frequency deviation (matching error) when V _E is 0.74V, 0.75V, 0.76V, and 0.77V in the circuit of FIG. The curve graphs of <X>, <Y>, and <Z> show the temperature characteristics of the oscillation frequency before temperature compensation, the temperature characteristics of the oscillation frequency after frequency correction at 85 ° C and 94.5 ° C, and 87.5 ° C, respectively. The temperature characteristics of the oscillation frequency after frequency correction at 92.5 ° C. are shown. When VE is in the range of _0.75V ± 0.01V, the temperature fluctuation range of the frequency deviation is suppressed to 10 ppb or less. That is, since the temperature characteristic of the frequency deviation is relatively insensitive to the value of _VE , it is not necessary to determine the value of _VE for each IC, and the voltage can be set in advance from the threshold voltage of the MOS transistor. be. As described above, it has been shown that the OCXO oscillation circuit using the temperature compensation circuit of the present invention shown in FIG. 1 can suppress the frequency fluctuation of the crystal oscillation circuit without temperature compensation to about 1/100.

FIG. 2 is a diagram showing a second embodiment of the present invention, and is a temperature compensation circuit for OCXO that utilizes the VG-ID (gate-source voltage-drain current) characteristic of the NOTE transistor. The basic configuration is the same as the temperature compensation circuit for OCXO using the VG-ID (gate-source voltage-drain current) characteristic of the polyclonal transistor described in FIG. The major difference between the OCXO temperature compensation circuit shown in FIG. 2 and the circuit of FIG. 1 is that the circuit that converts the output voltage V (BTO) of the non-inverting amplifier 54 into the voltage BTR based on the power supply voltage is omitted. Instead, the MIMO current is folded back by the current mirror circuits 83 and 84 to become ia1 and ia2, and the operating principle of the circuit is the same as that of the circuit of FIG. Further, if the MOS characteristics of the two NMOS transistors 71 and 73 are the same, the drain currents ia1 and ia2 are substantially symmetric with respect to the zero temperature special temperature. Further, Vgs can also be adjusted by applying a substrate voltage (backgate voltage), which is the same as the circuit of FIG. 1. As described above, the temperature compensation circuit of the present invention can use both the polyclonal transistor and the msgid transistor, and is highly versatile.

As described in detail above, since the temperature characteristic of the frequency deviation of the crystal oscillator behaves as a quadratic function at a temperature near the zero temperature special temperature, the present invention presents the present invention when the MOS transistor operates in the saturation region. Using the characteristic that the drain current is substantially proportional to the square of the gate voltage, the correction value corrected by the temperature compensation circuit of the present invention can be matched with the temperature characteristic of the frequency deviation of the crystal oscillator with a very good approximation. As a result, the frequency deviation of the clock signal from the VCXO oscillator can be made extremely small to about 10 ppb or less by the control voltage generated by using the temperature compensation circuit of the present invention, and it can be applied to high-speed communication of 5G to 6G. It goes without saying that the content can be applied to other parts of the specification without any contradiction even if the contents described and explained in a certain part of the specification are not described without any contradiction. Further, it is needless to say that the embodiment is an example and can be modified in various ways without departing from the gist, and the scope of rights of the present invention is not limited to the embodiment.

The temperature compensation circuit of the present invention is used for an OCXO or other oscillator using a constant temperature bath to provide an OCXO oscillator that can significantly reduce frequency fluctuations with respect to fluctuations in the internal temperature of the constant temperature bath due to changes in the environmental temperature. Can be provided. Furthermore, OCXO has excellent mass productivity because there is almost no deviation from the target frequency even if the set temperature of the constant temperature bath and the zero temperature special temperature of the crystal are not strictly adjusted (for example, the alignment accuracy is ± 0.1 ° C). An oscillator can be provided.

11 temperature sensor, 12 constant voltage source, 13 resistance, 14OP amplifier, 15 resistance, 16 resistance, 17 resistance, 18 resistance, 19OP amplifier, 21 resistance, 22 constant voltage source, 23 resistance (resistance R1), 24 resistance (resistance R2) ), 25 resistance (resistance R3), 26 constant voltage source, 27OP amplifier, 28OP amplifier, 29 resistance (resistance R4), 31PMOS transistor, 32 constant voltage source, 33PMOS transistor, 34 constant voltage source, 35 resistance, 36 voltage follower ( Buffer amplifier) circuit, 37 resistance, 38 resistance, 39 constant voltage source, 41OP amplifier, 51 temperature sensor, 52 constant voltage source, 53 resistance, 54OP amplifier, 55 resistance, 62 constant voltage source, 63 resistance (resistance R1), 64 Resistance (resistance R2), 65 resistance (resistance R3), 66 constant voltage source, 67OP amplifier, 68OP amplifier, 69 resistance (resistance R4), 71NMOS transistor, 72 constant voltage source, 73NMOS transistor, 74 constant voltage source, 75 resistance, 76 voltage follower (buffer amplifier) circuit, 77 resistance, 78 resistance, 79 constant voltage source, 81OP amplifier, 83 current mirror circuit, 84 current mirror circuit

Claims (9)

A temperature sensor that generates an output voltage that is a linear function of temperature, a non-inverting amplifier and an inverting amplifier that input the output of the temperature sensor, a MOS transistor that inputs the output of the non-inverting amplifier to the gate, and an output of the inverting amplifier. Is the MOS transistor input to the gate, the resistance to which the sum of the drain currents of the two MOS transistors flows, the constant voltage source connected to the source of the two MOS transistors, the buffer amplifier circuit of the voltage of the resistance, and the above. An oscillation circuit for OCXO (crystal oscillator with a constant temperature bath), which includes a VCXO (voltage controlled crystal oscillator) whose control voltage is the output of the buffer amplifier circuit. The oscillation circuit for OCXO according to claim 1, wherein the input voltage and the output voltage of the non-inverting amplifier are equal at a zero temperature special temperature (a temperature at which the frequency deviation becomes zero). The oscillation circuit for OCXO according to claim 1 or 2, wherein the input voltage and the output voltage of the inverting amplifier are equal at a zero temperature special temperature (a temperature at which the frequency deviation becomes zero). The feature is that the temperature characteristic straight line of the output voltage of the non-inverting amplifier and the temperature characteristic straight line of the output voltage of the inverting amplifier intersect at the zero temperature special temperature and have a substantially symmetric relationship with the intersecting voltage levels. The oscillator circuit for OCXO according to any one of claims 1 to 3. The oscillation circuit for OCXO according to any one of claims 1 to 4, wherein the amplification factors of the non-inverting amplifier and the inverting amplifier are variable. One of claims 1 to 5, wherein the voltage of the constant voltage source connected to the source of the MOS transistor can be changed so that the sum of the drain currents has a secondary characteristic of the temperature. The oscillation circuit for OCXO described in the section. The oscillator circuit for OCXO according to any one of claims 1 to 6, wherein the control voltage of the VCXO is generated from the sum of the voltage of the resistor and the constant voltage connected in series with the resistor. .. The oscillator circuit for OCXO according to any one of claims 1 to 7, wherein the two MOS transistors are both MOSFET transistors or both are nanotube transistors. The oscillator circuit for OCXO according to claim 8, wherein the two MOS transistors have substantially the same MOS current characteristics.

Images