Relaxation oscillator circuit

Abstract

According to the relaxation oscillator circuit, an average voltage feedback circuit is adopted to improve the frequency precision of the oscillator circuit, the stability of the oscillator circuit is improved, MOS transistors are adopted to form a reference voltage generation circuit, the device area is saved, the cost is reduced, meanwhile, circuit design parameters are easier to adjust, and a second-order or high-order filter is adopted to form an integrator. Noise of the oscillator can be filtered to the greatest extent, and the influence of temperature is avoided while the device area is saved.

Description

Technical Field

[0001] The utility model relates to an easy-to-calibrate high-precision relaxation oscillator circuit. Background Art

[0002] The relaxation oscillator is a commonly used on-chip oscillator structure. Traditional relaxation oscillator circuits such as Figure 1 As shown, the constant current source periodically charges the capacitor by alternately opening and closing switches S1 and S2, and then compares it with comparator A. comp The inverting input terminal of the oscillator is compared with the reference voltage, and the output terminal state changes periodically to generate a clock of a certain frequency. However, the frequency stability of the relaxation oscillator is not high, and the output frequency is easily affected by temperature and power supply voltage. In addition, the noise of internal devices will also affect the frequency, causing jitter.

[0003] The statements herein merely provide background technology related to the present invention and do not necessarily constitute prior art. Utility Model Content

[0004] The utility model aims to provide a relaxation oscillator circuit, which improves the frequency accuracy of the oscillator circuit, improves the stability of the oscillator circuit, saves device area, and reduces device cost.

[0005] In order to achieve the above object, the utility model provides a relaxation oscillator circuit, comprising:

[0006] An oscillator circuit comprises a first charge-discharge circuit and a second charge-discharge circuit which are symmetrically arranged, wherein the first charge-discharge circuit and the second charge-discharge circuit both comprise a MOS tube, a resistor and a capacitor;

[0007] The output control circuit comprises a first transmission gate TS1, a second transmission gate TS2, and a trigger D1, wherein one end of the first transmission gate TS1 is connected to the output end of the first charge-discharge circuit, and the other end is connected to the output end of the oscillator circuit, one end of the second transmission gate TS2 is connected to the output end of the second charge-discharge circuit, and the other end is connected to the output end of the oscillator circuit, and the trigger D1 is respectively connected to the first transmission gate TS1, the second transmission gate TS2, the first charge-discharge circuit, the second charge-discharge circuit, and a first comparator A comp1 The output of the second comparator A comp2 The output terminal;

[0008] The comparator circuit comprises a first comparator A comp1 and the second comparator A comp2 , the first comparator A comp1The positive input end is connected to the output end of the average voltage feedback circuit, the negative input end is connected to the output end of the first charge and discharge circuit, the output end is connected to the trigger D1, and the second comparator A comp2 The positive input end is connected to the output end of the average voltage feedback circuit, the negative input end is connected to the output end of the second charge and discharge circuit, and the output end is connected to the trigger D1;

[0009] The average voltage feedback circuit comprises an integrator and a reference voltage generating circuit, wherein the reference voltage generating circuit generates a reference voltage V ref The integrator has one input end connected to the reference voltage generating circuit, another input end connected to the output end of the oscillator circuit, and the output end connected to the first comparator A comp1 The positive input terminal of the second comparator A comp2 The positive input terminal.

[0010] The reference voltage generating circuit comprises a constant current source I and an NMOS tube M, the gate and drain of the NMOS tube M are connected, the constant current source I is connected in series to the drain of the NMOS tube M, the source of the NMOS tube M is grounded, and the drain of the NMOS tube M outputs a reference voltage V ref .

[0011] The integrator adopts a second-order active filter structure, which includes: a comparator A1, a first resistor R1, a second resistor R2, a first capacitor C1 and a second capacitor C2, and the positive input terminal of the comparator A1 is connected to a reference voltage V ref , the negative input terminal is connected to the output voltage V of the oscillator circuit osc The output terminal of the comparator A1 outputs a control voltage V c The first resistor R1 is connected in series to the negative input terminal of the comparator A1, the first capacitor C1 and the second capacitor C2 are connected in series between the negative input terminal and the output terminal of the comparator A1, one end of the second resistor R2 is connected between the first capacitor C1 and the second capacitor C2, and the other end is grounded.

[0012] The integrator adopts a two-stage cascade filter structure, which includes: a comparator A1, a first resistor R1, a second resistor R2, a first capacitor C1 and a second capacitor C2, and the positive input terminal of the comparator A1 is connected to a reference voltage V ref , the negative input terminal is connected to the output voltage V of the oscillator circuit osc The output terminal of the comparator A1 outputs a control voltage V cThe first resistor R1 and the second resistor R2 are connected in series at the negative input terminal of the comparator A1, one end of the first capacitor C1 is connected between the first resistor R1 and the second resistor R2, and the other end is grounded, and the second capacitor C2 is connected in series between the negative input terminal and the output terminal of the comparator A1.

[0013] The integrator adopts a high-order active filter structure, and the high-order active filter structure includes: an N-order filter, wherein N=3, 4, 5....k, and k is a natural number.

[0014] The utility model adopts an average voltage feedback circuit to improve the frequency accuracy of the oscillator circuit, improves the stability of the oscillator circuit, adopts a MOS tube to form a reference voltage generation circuit, saves device area, reduces costs and is easier to adjust circuit design parameters, adopts a second-order or high-order filter to form an integrator, can filter out the noise of the oscillator to the greatest extent, saves device area and is not affected by temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a circuit diagram of a relaxation oscillator in the background art.

[0016] Figure 2 The utility model discloses a circuit diagram of a relaxation oscillator circuit.

[0017] Figure 3 It is a curve diagram showing the relationship between oscillation frequency and temperature change.

[0018] Figure 4 is a circuit diagram of a reference voltage generating circuit.

[0019] Figure 5a The utility model provides a circuit diagram of a reference voltage generating circuit.

[0020] Figure 5b yes Figure 5a The relationship between the oscillation frequency of the circuit and the temperature change curve.

[0021] Figure 6a It is the circuit diagram of the integrator.

[0022] Figure 6b is the equivalent noise model of the oscillator.

[0023] Figure 7 yes Figure 6b Schematic diagram of the noise waveform.

[0024] Figure 8a The utility model provides a circuit diagram of a second-order active filter structure.

[0025] Figure 8bIt is a schematic diagram of the noise waveform of the first-order filter and the second-order filter.

[0026] Figure 9a The utility model provides a circuit diagram of a second-order cascade filter structure.

[0027] Figure 9b The utility model provides a circuit diagram of a high-order active filter structure. DETAILED DESCRIPTION

[0028] The following is based on Figure 2 9, a preferred embodiment of the present utility model is specifically described.

[0029] like Figure 2 As shown, the utility model provides a relaxation oscillator circuit, comprising:

[0030] An oscillator circuit comprises a first charge-discharge circuit and a second charge-discharge circuit which are symmetrically arranged, wherein the first charge-discharge circuit and the second charge-discharge circuit both comprise MOS tubes (M1-M4), a resistor R and a capacitor C;

[0031] The output control circuit comprises a first transmission gate TS1, a second transmission gate TS2, and a trigger D1, wherein one end of the first transmission gate TS1 is connected to the output end of the first charge-discharge circuit, and the other end is connected to the output end of the oscillator circuit, one end of the second transmission gate TS2 is connected to the output end of the second charge-discharge circuit, and the other end is connected to the output end of the oscillator circuit, and the trigger D1 is respectively connected to the first transmission gate TS1, the second transmission gate TS2, the first charge-discharge circuit, the second charge-discharge circuit, and a first comparator A comp1 The output of the second comparator A comp2 The output terminal;

[0032] The comparator circuit comprises a first comparator A comp1 and the second comparator A comp2 , the first comparator A comp1 The positive input end is connected to the output end of the average voltage feedback circuit, the negative input end is connected to the output end of the first charge and discharge circuit, the output end is connected to the trigger D1, and the second comparator A comp2 The positive input end is connected to the output end of the average voltage feedback circuit, the negative input end is connected to the output end of the second charge and discharge circuit, and the output end is connected to the trigger D1;

[0033] An average voltage feedback circuit (VAF) includes an integrator and a reference voltage generating circuit, wherein the reference voltage generating circuit generates a reference voltage V refThe integrator has one input end connected to the reference voltage generating circuit, another input end connected to the output end of the oscillator circuit, and the output end connected to the first comparator A comp1 The positive input terminal of the second comparator A comp2 The positive input terminal.

[0034] The first charge-discharge circuit and the second charge-discharge circuit are symmetrically arranged on the left and right sides, and the first voltage V output by the first charge-discharge circuit is transmitted by alternately switching the first transmission gate TS1 and the second transmission gate TS2 in one cycle. OSC1 and the second voltage V output by the second charge and discharge circuit OSC2 , the final output voltage of the oscillator circuit is V osc By the first voltage V OSC1 and the second voltage V OSC2 The summed voltage is used as the input of an average voltage feedback circuit, and the average voltage feedback circuit is used to improve the frequency accuracy of the oscillator circuit.

[0035] The oscillator circuit is fed by the average voltage feedback circuit output voltage V c Control, the oscillation frequency formula of the oscillator circuit (VCO) is: Among them, V dd is the power supply voltage. Due to the action of the integrator circuit in the average voltage feedback circuit, the final output voltage V osc The DC value is equal to the reference voltage V generated by the reference voltage generation circuit. ref ,Right now, Therefore, the frequency formula of the oscillator is updated to:

[0036]

[0037] First, from the perspective of temperature characteristics, the frequency formula of the oscillator circuit shows that the frequency of the oscillator is determined only by the resistance R, the capacitance C and the V ref / V dd The oscillation frequency decreases with the increase of the resistance R; when the power supply voltage V dd Under the condition of no change, with the reference voltage V ref As the resistance value of resistor R inevitably changes with temperature, the oscillation frequency will also drift due to the influence of temperature. Figure 3 As shown in Figure 1, when the oscillation frequency increases with the increase of temperature, a reference voltage with a positive temperature coefficient is required to offset the change of the oscillation frequency with temperature. Common reference voltage generation circuits are shown in Figure 1. Figure 4 As shown, the reference voltage V refThe voltage is generated by resistor series voltage division. The voltage division resistor is composed of a diffusion resistor with a positive temperature coefficient and a polysilicon resistor with a negative temperature coefficient in series. By changing the temperature coefficient of the voltage division resistor, a V ref Compensation voltage. However, there are three resistors in this circuit. When adjusting the resistance ratio between the resistors, the ratio of the resistance temperature coefficients must also be taken into account, and the parameter determination is relatively complicated.

[0038] like Figure 5a As shown, the utility model proposes an easily calibrated reference voltage generating circuit, the reference voltage generating circuit only includes: a constant current source I and an NMOS tube M, the gate and drain of the NMOS tube M are connected, the constant current source I is connected in series to the drain of the NMOS tube M, the source of the NMOS tube M is grounded, and the drain of the NMOS tube M outputs a reference voltage V ref .like Figure 5b As shown, when a relatively large bias current flows through the gate-drain connected NMOS tube M, its gate-source voltage V GS It increases with the increase of temperature, has a linear first-order positive temperature coefficient, and is affected by the power supply voltage V dd The influence is small. Adjusting the constant current source current I can change the positive and negative temperature characteristics of the NMOS tube M connected to the gate and drain, and adjusting the aspect ratio of the NMOS tube M can change the gate-source voltage V GS The slope of the temperature characteristic curve. Compared with the commonly used circuit that uses resistors with positive and negative temperature coefficients in series as reference voltage generation, the circuit that uses MOS tubes as reference voltage generation saves more area, reduces costs, and is easier to adjust circuit design parameters.

[0039] Next, we analyze from the perspective of noise characteristics. Figure 2 In the oscillator structure shown, the main noise comes from the comparator in the oscillator. The only way to suppress the comparator noise is to increase the device size of the comparator (to reduce flicker noise) and the bias current (to reduce thermal noise). However, the large bias current causes large power consumption, and the large device size increases the parasitic capacitance, which makes the delay t of the comparator d It is more susceptible to the influence of temperature and power supply voltage, thus affecting the accuracy of the oscillator. The integrator in the average voltage feedback circuit (VAF) is used to filter the noise of the comparator. Figure 6a It is a traditional integrator structure, and the feedback circuit is replaced by capacitor C1. Figure 6b is the oscillator equivalent noise model, where K VCO is the frequency gain, V osc,dc With control voltage V C Proportional, the proportionality coefficient is β. n The noise of the average voltage feedback circuit (VAF) comes from the amplifier itself. nThe negative feedback loop formed by the average voltage feedback circuit (VAF) structure is equivalent to a first-order active high-pass filter for the noise transfer function characteristics of the oscillator, which can suppress the low-frequency phase noise of the oscillator to a certain extent (such as Figure 7 As shown in Figure 1). However, the first-order active filter has a limited degree of noise attenuation. If the size of the comparator is very small, its own noise will still have a certain impact on the frequency of the oscillator.

[0040] The utility model adopts a second-order active filter structure to replace the first-order active filter, which can further suppress the phase noise of the oscillator. Figure 8a As shown, the second-order active filter structure includes: a comparator A1, a first resistor R1, a second resistor R2, a first capacitor C1 and a second capacitor C2, and the positive input terminal of the comparator A1 is connected to a reference voltage V ref , the negative input terminal is connected to the output voltage V of the oscillator circuit osc The output terminal of the comparator A1 outputs a control voltage V c , the first resistor R1 is connected in series to the negative input terminal of the comparator A1, the first capacitor C1 and the second capacitor C2 are connected in series between the negative input terminal and the output terminal of the comparator A1, one end of the second resistor R2 is connected between the first capacitor C1 and the second capacitor C2, and the other end is grounded. Figure 8b As shown, compared with the first-order filter, the second-order filter structure has a narrower transition band and can attenuate the oscillator noise faster, further suppressing the oscillator's phase noise. As a result, the size parameters of the comparator can be made smaller, alleviating the negative impact of temperature on the device's parasitic parameters.

[0041] In addition to using a second-order filter, the utility model also provides Figure 9a The second-order cascade filter structure shown in FIG. Figure 9b The high-order active filter structure shown can also attenuate the noise faster and further ease the selection of comparator parameter design.

[0042] like Figure 9a As shown, the second-order cascade filter structure includes: a comparator A1, a first resistor R1, a second resistor R2, a first capacitor C1 and a second capacitor C2, and the positive input terminal of the comparator A1 is connected to a reference voltage V ref , the negative input terminal is connected to the output voltage V of the oscillator circuit osc The output terminal of the comparator A1 outputs a control voltage V cThe first resistor R1 and the second resistor R2 are connected in series at the negative input terminal of the comparator A1, one end of the first capacitor C1 is connected between the first resistor R1 and the second resistor R2, and the other end is grounded, and the second capacitor C2 is connected in series between the negative input terminal and the output terminal of the comparator A1.

[0043] like Figure 9b As shown, the high-order active filter structure includes: an N-order filter, wherein N=3, 4, 5....k, and k is a natural number.

[0044] After the utility model improves the integrator, the noise of the comparator can be filtered out to a great extent, so that the comparator can be designed to be smaller in size, saving area and not being affected by temperature. The better the noise filtering effect of the integrator is, the easier the design of the comparator is, the less affected by temperature, and the more stable the performance of the entire oscillator is.

[0045] The utility model provides a relaxation oscillator circuit, which adopts an average voltage feedback circuit to improve the frequency accuracy of the oscillator circuit, improves the stability of the oscillator circuit, adopts a MOS tube to form a reference voltage generation circuit, saves device area, reduces costs and is easier to adjust circuit design parameters, adopts a second-order or high-order filter to form an integrator, can filter out the noise of the oscillator to the greatest extent, saves device area and is not affected by temperature.

[0046] It should be noted that, in the embodiments of the present invention, the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the embodiments, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limitations on the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0047] In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0048] It should be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0049] It should also be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the application. As used in this application specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0050] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0051] As used in this specification and the appended claims, the term "if" may be interpreted as "when" or "upon" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if [described condition or event] is detected" may be interpreted as meaning "upon determination" or "in response to determining" or "upon detection of [described condition or event]" or "in response to detecting [described condition or event]," depending on the context.

[0052] Although the content of the utility model has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the utility model. Obviously, the described embodiments are only a part of the embodiments of the utility model, not all of them. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the utility model. After reading the above content, various modifications and substitutions of the utility model will be obvious to those skilled in the art. Therefore, the scope of protection of the utility model should be defined by the attached claims.

Claims

1. A relaxation oscillator circuit, characterized in that: Contains: oscillator circuit, output control circuit, comparator circuit and average voltage feedback circuit; The oscillator circuit comprises a first charge-discharge circuit and a second charge-discharge circuit which are symmetrically arranged, and the first charge-discharge circuit and the second charge-discharge circuit both comprise a MOS tube, a resistor and a capacitor; The output control circuit comprises a first transmission gate TS1, a second transmission gate TS2, and a trigger D1. One end of the first transmission gate TS1 is connected to the output end of the first charge-discharge circuit, and the other end is connected to the output end of the oscillator circuit. One end of the second transmission gate TS2 is connected to the output end of the second charge-discharge circuit, and the other end is connected to the output end of the oscillator circuit. The trigger D1 is respectively connected to the first transmission gate TS1, the second transmission gate TS2, the first charge-discharge circuit, the second charge-discharge circuit, and the first comparator A. comp1 The output of the second comparator A comp2 The output terminal; The comparator circuit comprises a first comparator A comp1 and the second comparator A comp2 , the first comparator A comp1 The positive input end is connected to the output end of the average voltage feedback circuit, the negative input end is connected to the output end of the first charge and discharge circuit, the output end is connected to the trigger D1, and the second comparator A comp2 The positive input end is connected to the output end of the average voltage feedback circuit, the negative input end is connected to the output end of the second charge and discharge circuit, and the output end is connected to the trigger D1; The average voltage feedback circuit includes an integrator and a reference voltage generating circuit, wherein the reference voltage generating circuit generates a reference voltage V ref The integrator has one input end connected to the reference voltage generating circuit, another input end connected to the output end of the oscillator circuit, and the output end connected to the first comparator A comp1 The positive input terminal of the second comparator A comp2 The positive input terminal.

2. The relaxation oscillator circuit according to claim 1, wherein: The reference voltage generating circuit comprises a constant current source I and an NMOS tube M, the gate and drain of the NMOS tube M are connected, the constant current source I is connected in series to the drain of the NMOS tube M, the source of the NMOS tube M is grounded, and the drain of the NMOS tube M outputs a reference voltage V ref .

3. The relaxation oscillator circuit according to claim 1, wherein: The integrator adopts a second-order active filter structure, which includes: a comparator A1, a first resistor R1, a second resistor R2, a first capacitor C1 and a second capacitor C2, and the positive input terminal of the comparator A1 is connected to a reference voltage V ref , the negative input terminal is connected to the output voltage V of the oscillator circuit osc The output terminal of the comparator A1 outputs a control voltage V c The first resistor R1 is connected in series to the negative input terminal of the comparator A1, the first capacitor C1 and the second capacitor C2 are connected in series between the negative input terminal and the output terminal of the comparator A1, one end of the second resistor R2 is connected between the first capacitor C1 and the second capacitor C2, and the other end is grounded.

4. The relaxation oscillator circuit according to claim 1, wherein: The integrator adopts a two-stage cascade filter structure, which includes: a comparator A1, a first resistor R1, a second resistor R2, a first capacitor C1 and a second capacitor C2, and the positive input terminal of the comparator A1 is connected to a reference voltage V ref , the negative input terminal is connected to the output voltage V of the oscillator circuit osc The output terminal of the comparator A1 outputs a control voltage V c , the first resistor R1 and the second resistor R2 are connected in series to the negative input end of the comparator A1, one end of the first capacitor C1 is connected between the first resistor R1 and the second resistor R2, and the other end is grounded, The second capacitor C2 is connected in series between the negative input terminal and the output terminal of the comparator A1.

5. The relaxation oscillator circuit according to claim 1, wherein: The integrator adopts a high-order active filter structure, and the high-order active filter structure includes: an N-order filter, wherein: N=3, 4, 5....k, k is a natural number.

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