Reference current generating circuit

Abstract

The invention provides a reference current generating circuit which comprises a reference voltage generating circuit and a current source circuit. The reference voltage generating circuit is used for generating a first reference voltage according to the first current. The reference voltage generating circuit includes a native transistor element, and the first current flows through the native transistor element. The current source circuit is coupled to the reference voltage generating circuit. The current source circuit is used for generating a reference current according to a first reference voltage. The current source circuit includes a cascode transistor circuit, and a reference current flows through the cascode transistor circuit. The cascode transistor circuit includes a low voltage transistor component and a high voltage transistor component coupled in series.

Description

Technical Field

[0001] The present invention relates to a reference current generating circuit, and more particularly to a reference current generating circuit applied to an oscillator circuit. Background Art

[0002] An oscillator circuit is usually required in the processor circuit of a magnetoresistive sensor to perform the counting function. For example, when the ultra-slow oscillator used for counting operates at a frequency of 1 Hz, the circuit is only started once per second and enters sleep mode at other times. In this application scenario, the accuracy of the oscillator circuit's counting function is very important. If the oscillation signal generated by the oscillator circuit is easily changed with temperature and voltage, the counting accuracy will be reduced. Summary of the invention

[0003] The invention provides a reference current generating circuit. The reference current and the reference voltage generated by the reference current generating circuit are not easily changed with the temperature. Therefore, when applied to an oscillator circuit, the accuracy of the oscillator circuit can be improved.

[0004] The reference current generating circuit of the present invention includes a reference voltage generating circuit and a current source circuit. The reference voltage generating circuit is used to generate a first reference voltage according to a first current. The reference voltage generating circuit includes a native transistor component, and the first current flows through the native transistor component. The current source circuit is coupled to the reference voltage generating circuit. The current source circuit is used to generate a reference current according to the first reference voltage. The current source circuit includes a cascade transistor circuit, and the reference current flows through the cascade transistor circuit. The cascade transistor circuit includes a low voltage transistor component and a high voltage transistor component coupled in series.

[0005] In order that the foregoing may be better understood, several embodiments are described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and together with the description serve to explain the principles of the present disclosure.

[0007] Figure 1 A schematic diagram showing the structure of a reference current generating circuit according to an embodiment of the present invention;

[0008] Figure 2 A schematic diagram showing the variation of the critical voltage of the low voltage transistor component and the high voltage transistor component with temperature according to the present embodiment;

[0009] Figure 3 A schematic diagram showing an oscillator circuit according to an embodiment of the present invention.

[0010] Description of Figure Numbers

[0011] 100: reference current generating circuit;

[0012] 110: reference voltage generating circuit;

[0013] 120: Current source circuit;

[0014] 122: Stacked transistor circuit;

[0015] 210, 220, 230: straight line;

[0016] 300: oscillator circuit;

[0017] GND: second voltage;

[0018] I0: first current;

[0019] IREF: reference current;

[0020] MN0: native transistor component;

[0021] MN1: fourth transistor component;

[0022] MN6: low voltage transistor assembly;

[0023] MN7: High voltage transistor assembly;

[0024] MP1: second transistor component;

[0025] MP2: third transistor component;

[0026] MP3: first transistor assembly;

[0027] T: temperature;

[0028] t: time;

[0029] V: voltage;

[0030] VBG: first reference voltage;

[0031] VDD: first voltage;

[0032] VREF: second reference voltage, reference voltage;

[0033] VX: Oscillation signal. DETAILED DESCRIPTION

[0034] Figure 1 FIG. 1 is a schematic diagram showing the structure of a reference current generating circuit according to an embodiment of the present invention. Figure 1The reference current generating circuit 100 of the present embodiment includes a reference voltage generating circuit 110 and a current source circuit 120. The reference voltage generating circuit 110 is used to generate a first reference voltage VBG (i.e., a reference voltage) according to a first current I0. The reference voltage generating circuit 100 includes a native transistor element MN0. The first current I0 flows through the native transistor element MN0. The native transistor element is a transistor element whose threshold voltage approaches 0 volts (voltage, V).

[0035] The current source circuit 120 is coupled to the reference voltage generating circuit 110. The current source circuit 120 is used to generate a reference current IREF according to a first reference voltage VBG. The current source circuit 120 includes a cascade transistor circuit 122. The reference current flows through the cascade transistor circuit 122. The cascade transistor circuit 120 includes a low voltage transistor element MN6 and a high voltage transistor element MN7 coupled in series. The low voltage transistor element is a transistor element with a lower threshold voltage and a lower withstand voltage, for example, Vt=0.4V, and VDD is 1.8V at maximum. The high voltage transistor element is a transistor element with a higher threshold voltage and a higher withstand voltage, for example, Vt=0.7V, and VDD is 3.3V at maximum.

[0036] Specifically, the current source circuit 120 further includes a first transistor component MP3. The first transistor component MP3 has a first terminal, a second terminal and a control terminal. The first terminal of the first transistor component MP3 is coupled to a first voltage VDD (system high voltage), the second terminal of the first transistor component is coupled to the cascade transistor circuit 122, and the control terminal of the first transistor component MP3 is coupled to the second terminal of the first transistor component MP3.

[0037] The low voltage transistor element MN6 has a first terminal, a second terminal and a control terminal. The first terminal of the low voltage transistor element MN6 is coupled to the second terminal of the first transistor element MP3 , and the control terminal of the low voltage transistor element MN6 is coupled to the reference voltage generating circuit 110 .

[0038] The high-voltage transistor component MN7 has a first terminal, a second terminal and a control terminal. The first terminal of the high-voltage transistor component MN7 is coupled to the second terminal of the low-voltage transistor component MN6, the second terminal of the high-voltage transistor component MN7 is coupled to the second voltage GND (system low voltage), and the control terminal of the high-voltage transistor component MN7 is coupled to the reference voltage generating circuit 110. The high-voltage transistor component MN7 operates in the subcritical region.

[0039] The control terminal of the low voltage transistor element MN6 and the control terminal of the high voltage transistor element MN7 receive the first reference voltage VBG and are controlled by the first reference voltage VBG. The reference current IREF flows through the first transistor element MP3, the low voltage transistor element MN6 and the high voltage transistor element MN7 in sequence to generate a second reference voltage VREF at the first terminal of the high voltage transistor element MN7.

[0040] In this embodiment, the second reference voltage VREF is less affected by temperature changes, as described below. Figure 2 A schematic diagram showing the variation of the critical voltage of the low-voltage transistor component and the high-voltage transistor component of the present embodiment with temperature is shown. A straight line 210 shows that the critical voltage Vth7 of the high-voltage transistor component MN7 decreases with temperature variation, and a straight line 220 shows that the critical voltage Vth6 of the low-voltage transistor component MN6 decreases with temperature variation, wherein the vertical axis is voltage in volts, and the horizontal axis is absolute temperature in kelvins (K).

[0041] The second reference voltage VREF can be expressed by the following formula:

[0042] VREF=(Vth7-Vth6)+VT×ln(S6 / S7)

[0043] Among them, VREF is the second reference voltage; Vth6 and Vth7 are the critical voltages of the low-voltage transistor component MN6 and the high-voltage transistor component MN7 respectively; S6 and S7 are the S parameters of the low-voltage transistor component MN6 and the high-voltage transistor MN7 respectively, where S = (W / L)Cox, L is the channel length of the transistor, W is the channel width of the transistor, and Cox is the gate oxide layer capacitance of the transistor; VT is the thermal voltage, approximately 0.026 volts; and ln(S6 / S7) is the natural logarithm of S6 divided by S7.

[0044] Depend on Figure 2 It can be seen that since the difference Vth7-Vth6 (ie, straight line 230) between the threshold voltages Vth6 and Vth7 of the low voltage transistor element MN6 and the high voltage transistor element MN7 is fixed and does not change with temperature, the second reference voltage VVREF is less affected by temperature changes.

[0045] In this embodiment, the high-voltage transistor device MN7 operates in a subthreshold or weak-inversion region, and its drain current ID can be expressed as:

[0046]

[0047] Wherein, ID is the drain current of the transistor; the parameter of the transistor S = (W / L)Cox, where L is the channel length of the transistor, W is the channel width of the transistor, and Cox is the gate oxide capacitance of the transistor; μ is the carrier mobility; exp() is an exponential function with the natural constant e as the base; VT is the thermal voltage, which is approximately 0.026 volts; VGS is the gate and source voltage difference of the transistor; Vth is the threshold voltage of the transistor; and m is the subthreshold slope parameter.

[0048] Since the reference current IREF flows through the first transistor element MP3, the low voltage transistor element MN6 and the high voltage transistor element MN7 in sequence, the reference current IREF is substantially equal to the drain current ID of the high voltage transistor element MN7. Therefore, the magnitude of the reference current IREF is also determined by the above current formula.

[0049] In the above current formula, when the temperature T rises, the carrier mobility μ will decrease, the gate-source voltage difference VGS of the transistor will decrease, the critical voltage Vth will decrease, the sub-critical slope parameter m will increase, the thermal voltage VT will increase, and the overall value of the exponential function exp() will decrease. Therefore, this embodiment can appropriately design the size of the high-voltage transistor component MN7 (i.e., the transistor parameter S) so that the reference current IREF is less affected by temperature changes within a certain temperature range.

[0050] On the other hand, please refer to Figure 1 The reference voltage generating circuit 110 further includes a second transistor component MP1, a third transistor component MP2 and a fourth transistor component MN1. The second transistor component MP1 has a first terminal, a second terminal and a control terminal. The first terminal of the second transistor component MP1 is coupled to the first voltage VDD, and the second terminal of the second transistor component MP1 is coupled to the control terminal of the second transistor component MP1.

[0051] The third transistor element MP2 has a first terminal, a second terminal and a control terminal. The first terminal of the third transistor element MP2 is coupled to the first voltage VDD, and the control terminal of the third transistor element MP2 is coupled to the control terminal of the second transistor element MP1.

[0052] The fourth transistor element MN1 has a first terminal, a second terminal and a control terminal. The first terminal of the fourth transistor element MN1 is coupled to the second terminal of the third transistor element MP2, the second terminal of the fourth transistor element MN1 is coupled to the second voltage GND, and the control terminal of the fourth transistor element MN1 is coupled to the first terminal of the fourth transistor element MN1. The first terminal of the fourth transistor element MN1 is coupled to the current source circuit 120, and the first reference voltage VBG is generated at the first terminal of the fourth transistor element MN1 and output to the current source circuit 120 through the first terminal of the fourth transistor element MN1.

[0053] The native transistor element MN0 has a first terminal, a second terminal and a control terminal. The first terminal of the native transistor element MN0 is coupled to the second terminal of the second transistor element MP1, and the second terminal and the control terminal of the native transistor element MN0 are coupled to the second voltage GND. The native transistor element MN0 operates in the saturation region.

[0054] In this embodiment, since the native transistor element MN0 operates in the saturation region, the first current I0 can be expressed as:

[0055]

[0056] Among them, I0 is the drain current of the transistor; the parameter of the transistor S = 1 / 2μCox, where μ is the carrier mobility and Cox is the gate oxide capacitance of the transistor; L is the channel length of the transistor, W is the channel width of the transistor; VGS is the gate and source voltage difference of the transistor; and Vth is the threshold voltage of the transistor, which is about -0.1V. In addition, since the VGS of the native transistor component MN0 is 0, the above current formula can be simplified to:

[0057]

[0058] From the above current formula, it can be seen that the first current I0 is a current that is independent of the first voltage VDD and is not easily changed by the first voltage VDD. Since the first current I0 is not easily changed by the first voltage VDD, the reference voltage generating circuit 110 can also generate a more accurate first reference voltage VBG (ie, reference voltage).

[0059] In addition, Figure 1 In the embodiment, except for the native transistor element MN0 operating in the saturation region, the other transistor elements operate in the subcritical region.

[0060] Figure 3 FIG. 2 is a schematic diagram showing an oscillator circuit according to an embodiment of the present invention. Figure 1 and Figure 3 , Figure 1The reference current IREF of the reference current generating circuit 100 of the embodiment can be applied to Figure 3 The oscillator circuit 300 is used to provide a reference current IREF to the oscillator circuit 300, and the second reference voltage VREF generated by the reference current generating circuit 100 can also be used as a reference voltage of the oscillator circuit 300. The oscillator circuit 300 generates an oscillation signal VX according to the reference current IREF and the reference voltage VREF, and its waveform is a sawtooth wave (triangle wave) that changes with time t. Since the reference current IREF is less affected by temperature changes, the oscillation signal VX is also less affected by temperature changes.

[0061] also, Figure 3 The oscillator circuit 300 can be applied to processor circuits of various magnetoresistive sensors such as a tunnel magnetoresistance (TMR) sensor, a giant magnetoresistance (GMR) sensor, or anisotropic magnetoresistance (AMR) sensor as a low-speed oscillator.

[0062] In summary, in the embodiments of the present invention, the reference voltage generating circuit can generate a more accurate reference voltage, and by appropriately designing the size of the high voltage transistor component of the current source circuit, the reference current is less affected by temperature changes within a certain temperature range. In addition, the reference current and reference voltage generated by the reference current generating circuit are not easily changed with temperature, so when applied to an oscillator circuit, the accuracy of the oscillator circuit can be improved.

[0063] It will be apparent to those skilled in the art that various modifications and variations may be made to the disclosed embodiments without departing from the scope or spirit of the present disclosure. In view of the foregoing, it is intended that the present disclosure encompass modifications and variations provided that the modifications and variations fall within the scope of the appended claims and their equivalents.

Claims

1. A reference current generating circuit, comprising: a reference voltage generating circuit, configured to generate a first reference voltage according to a first current, wherein the reference voltage generating circuit comprises a native transistor component, and the first current flows through the native transistor component; as well as a current source circuit coupled to the reference voltage generating circuit and configured to generate a reference current according to the first reference voltage, wherein the current source circuit comprises a cascade transistor circuit, and the reference current flows through the cascade transistor circuit; The cascade transistor circuit includes a low voltage transistor component and a high voltage transistor component coupled in series. 2 . The reference current generating circuit according to claim 1 , wherein the native transistor element operates in a saturation region. 3 . The reference current generating circuit according to claim 1 , wherein the high voltage transistor device operates in a subcritical region.

4. The reference current generating circuit according to claim 1, wherein the current source circuit further comprises: A first transistor component has a first end, a second end and a control end, wherein the first end of the first transistor component is coupled to a first voltage, the second end of the first transistor component is coupled to the cascaded transistor circuit, and the control end of the first transistor component is coupled to the second end of the first transistor component.

5. The reference current generating circuit according to claim 4, wherein The low voltage transistor component has a first end, a second end and a control end, wherein the first end of the low voltage transistor component is coupled to the second end of the first transistor component, and the control end of the low voltage transistor component is coupled to the reference voltage generating circuit; and The high-voltage transistor component has a first end, a second end and a control end, wherein the first end of the high-voltage transistor component is coupled to the second end of the low-voltage transistor component, the second end of the high-voltage transistor component is coupled to a second voltage, and the control end of the high-voltage transistor component is coupled to the reference voltage generating circuit. 6 . The reference current generating circuit according to claim 5 , wherein the control terminal of the low voltage transistor element and the control terminal of the high voltage transistor element receive the first reference voltage and are controlled by the first reference voltage. 7 . The reference current generating circuit according to claim 5 , wherein the reference current flows through the first transistor element, the low voltage transistor element and the high voltage transistor element in sequence.

8. The reference current generating circuit as claimed in claim 5, wherein a second reference voltage is generated at the first terminal of the high voltage transistor element.

9. The reference current generating circuit according to claim 1, wherein the reference voltage generating circuit further comprises: a second transistor component having a first terminal, a second terminal and a control terminal, wherein the first terminal of the second transistor component is coupled to a first voltage, and the second terminal of the second transistor component is coupled to the control terminal of the second transistor component; a third transistor component having a first terminal, a second terminal and a control terminal, wherein the first terminal of the third transistor component is coupled to the first voltage, and the control terminal of the third transistor component is coupled to the control terminal of the second transistor component; and a fourth transistor component having a first terminal, a second terminal and a control terminal, wherein the first terminal of the fourth transistor component is coupled to the second terminal of the third transistor component, the second terminal of the fourth transistor component is coupled to a second voltage, and the control terminal of the fourth transistor component is coupled to the first terminal of the fourth transistor component, The native transistor component has a first terminal, a second terminal and a control terminal, the first terminal of the native transistor component is coupled to the second terminal of the second transistor component, and the second terminal and the control terminal of the native transistor component are coupled to the second voltage.

10. The reference current generating circuit according to claim 9, wherein the first end of the fourth transistor component is coupled to the current source circuit, and the first reference voltage is generated at the first end of the fourth transistor component and output to the current source circuit through the first end of the fourth transistor component.

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