Differential cross-coupled multivibrator

Abstract

The invention belongs to the field of analog integrated circuit design, and particularly relates to a differential cross-coupled multivibrator, which comprises an oscillation main circuit used for generating periodic rectangular waves; the control voltage selection circuit is used for realizing frequency adjustment of the oscillation main circuit by selecting a control voltage; the control voltage buffer circuit is used for suppressing power supply noise interference in the oscillation main circuit and assisting the control voltage selection circuit to realize frequency adjustment; by introducing the control voltage selection circuit, the frequency of the oscillator can be changed along with the change of the voltage, so that the effect of the voltage-controlled oscillator is realized; a control voltage buffer circuit is introduced to reduce power supply noise and reduce the influence of process deviation.

Description

Technical Field

[0001] This invention belongs to the field of analog integrated circuit design, and further relates to the field of voltage-controlled oscillators, specifically to a differential cross-coupled multivibrator. Background Technology

[0002] An emitter-coupled multivibrator is an astable, self-oscillating circuit based on a transistor symmetric structure. Its core operating principle relies on the alternating conduction of two cross-coupled transistors, causing current redistribution. This redistribution, through the charging and discharging of the coupling capacitor, results in state reversal, creating a continuous square wave oscillation. It is widely used in low-frequency pulse generation, digital circuit clocks, and timers. Currently, emitter-coupled multivibrators have the following drawbacks:

[0003] The oscillation frequency can only be adjusted by adjusting the capacitor, resistor or current parameters, and the frequency cannot be directly controlled by voltage, so it is difficult to achieve voltage-controlled oscillation function.

[0004] Circuit performance is susceptible to power supply noise interference. Summary of the Invention

[0005] To address the above problems, this invention provides a differential cross-coupled multivibrator, comprising:

[0006] The main oscillation circuit is used to generate periodic rectangular waves;

[0007] A control voltage selection circuit is used to adjust the frequency of the oscillation main circuit by selecting a control voltage.

[0008] The control voltage buffer circuit is used to suppress power supply noise interference in the main oscillation circuit and assists the control voltage selection circuit in achieving frequency regulation.

[0009] The beneficial effects of this invention are:

[0010] This invention introduces a control voltage selection circuit, which enables the oscillator frequency to change with the voltage, thus achieving the effect of a voltage-controlled oscillator.

[0011] This invention introduces a control voltage buffer circuit to reduce power supply noise and minimize the impact of process deviations.

[0012] The circuit structure of this invention is simple, easy to implement, and applicable to most processes. Attached Figure Description

[0013] Figure 1 It is a traditional emitter-coupled multivibrator;

[0014] Figure 2The static IV characteristic curves of the capacitor at both ends of a traditional emitter-coupled multivibrator are shown.

[0015] Figure 3 This invention relates to a differential cross-coupled multivibrator;

[0016] Figure 4 The output simulation results of the differential cross-coupled multivibrator of this invention are shown below.

[0017] Figure 5 The output frequency simulation results for different control voltages in embodiments of the present invention are shown. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Figure 1 The circuit shown is an emitter-coupled multivibrator, consisting of transistors, resistors, capacitors, and current sources. Depending on the parameter configuration (especially the value of capacitor C), this circuit can exhibit two distinct operating modes: relaxation oscillator mode and near-sinusoidal LC oscillator mode. When capacitor C is large, the circuit operates in relaxation oscillator mode; while when capacitor C is small, it operates in near-sinusoidal LC oscillator mode. Since emitter-coupled multivibrators are primarily used to generate clock signals, this invention will only discuss the relaxation oscillator mode.

[0020] In relaxation oscillator mode, its basic working principle can be described as follows: Considering the two ends of the capacitor C as a nonlinear two-port network, its characteristic curve can be derived to be S-shaped, such as... Figure 2 As shown, I represents the current flowing through capacitor C, and V represents the voltage across capacitor C. The essence of relaxation oscillation is the repeated charging and discharging process of a capacitor between two unstable critical points. A complete working cycle can be divided into the following four stages:

[0021] Phase 1 (Capacitor charging, from point D to point A): Assume that the circuit is initially operating at point D on the upper right branch of the S-curve. At this time, Q2 is close to being cut off, while Q1 conducts most of the current. The capacitor C begins to charge through the left path (i.e., the path composed of the resistor and current source connected by Q5, Q1, and Q1). The operating point slowly moves along the DA segment of the S-curve, the voltage V changes slowly, and the current remains basically constant.

[0022] Phase Two (Rapid Transition, from Point A to Point B): When the operating point reaches the critical point A, the system equilibrium is disrupted. Based on Mandelstam's "discontinuity theory," the circuit state will undergo an infinitely rapid transition, instantaneously jumping from point A to point B, with the current changing from I... C Mutation to -I C .

[0023] Phase 3 (Capacitor Discharge, from Point B to Point C): After the transition, the circuit enters point B of the lower left branch of the S-curve. Capacitor C begins to discharge in reverse, the operating point slowly moves along segment BC, the voltage V changes slowly in the opposite direction, and the current remains near -IC.

[0024] Phase 4 (Rapid jump, from point C to point D): When the operating point reaches another critical point C, a rapid jump occurs again, instantly returning from point C to point D, thus completing a full oscillation cycle.

[0025] Among them, I C The emitter current of the specially turned-on transistor (approximately constant) is as follows:

[0026] When transistor Q1 is turned on and transistor Q2 is turned off, I C ≈ Emitter current of transistor Q1;

[0027] When transistor Q2 is turned on and transistor Q1 is turned off, I C ≈ Emitter current of transistor Q2 (the current direction is opposite to the former, so it is denoted as -I) C ).

[0028] The emitter current of the transistor is provided by a current source.

[0029] Figure 1 The frequency of the emitter-coupled multivibrator shown in relaxation oscillator mode is:

[0030]

[0031] I0 is the current value of the current source, C is the capacitance value, and V BE（ON） It is the turn-on voltage of transistors Q1 and Q2 (related to R in the circuit and the current source current I0).

[0032] However, the above-mentioned emitter-coupled multivibrator has the following drawbacks:

[0033] The oscillation frequency can only be adjusted by changing the capacitor, resistor, or current parameters; it cannot be directly controlled by voltage, making it difficult to achieve voltage-controlled oscillation (VCO) functionality. Furthermore, the circuit performance is susceptible to power supply noise interference.

[0034] Therefore, this invention proposes a differential cross-coupled multivibrator, comprising:

[0035] The main oscillation circuit is used to generate periodic rectangular waves;

[0036] A control voltage selection circuit is used to adjust the frequency of the oscillation main circuit by selecting a control voltage.

[0037] The control voltage buffer circuit is used to suppress power supply noise interference in the main oscillation circuit and assists the control voltage selection circuit in achieving frequency regulation.

[0038] In some embodiments, to solve Figure 1 In the emitter-coupled oscillator circuit shown, VDD noise directly interferes with the base-emitter voltage (VBE) of Q1 and Q2 through the coupling of transistors Q1~Q6. (ON) To address the issue of the resonant frequency being affected, this invention adds a control voltage buffer circuit composed of Q7~Q10, with the structure as follows: Figure 3 As shown, it includes:

[0039] The bases of transistors Q7 to Q8 are connected to capacitor C1 in the control voltage selection circuit, and the connection point is denoted as V1. The collector of transistor Q7 is connected to the power supply voltage, and the emitter of transistor Q7 is connected to the base of transistor Q9 and the main oscillation circuit. The collector of transistor Q9 is grounded, and the emitter of transistor Q9 is connected to the emitter of transistor Q10, and the connection point is denoted as V2. The emitters of transistors Q9 to Q10 are also connected to the main oscillation circuit. The collector of transistor Q8 is grounded. The emitter of transistor Q8 is connected to the main oscillation circuit, as well as the base and collector of transistor Q10. The collector of transistor Q10 is connected to the power supply voltage.

[0040] This voltage buffer circuit can effectively isolate VDD noise from VBE of Q1 and Q2 via coupling through Q1~Q6. (ON) The initial control voltage Vin is provided by the reference circuit, which has a high power supply rejection ratio, further suppressing the interference of VDD noise on the resonant frequency.

[0041] In some embodiments, to overcome the limitation of the non-adjustable frequency of traditional emitter-coupled multivibrators, this invention introduces a control voltage selection circuit. Different control voltages are selected via switches S1, S2, and S3 to adjust the oscillation frequency. The specific circuit is as follows: Figure 3 As shown, it includes switches S1~S3, resistors R1~R4, and capacitor C1, wherein:

[0042] One end of resistor R1 is connected to voltage Vin, and the other end of resistor R1 is connected to one end of resistor R2; the other end of resistor R2 is connected to one end of resistor R3, the other end of resistor R3 is connected to resistor R4, and the other end of resistor R4 is grounded.

[0043] Switch S1 is connected across resistor R2, switch S2 is connected across resistor R3, and switch S3 is connected across resistor R4.

[0044] One end of the capacitor is connected to one end of the resistor R2 and the control voltage buffer circuit; the other end of the capacitor C1 is grounded.

[0045] In some embodiments, resistors R2 to R4 have the same resistance value, and the resistance value of resistor R1 is twice that of resistor R2.

[0046] In the control voltage selection circuit, switches S1, S2, and S3 are used to select the corresponding initial control voltage. This voltage is transmitted to node V2 via a control voltage buffer circuit composed of transistors Q7 to Q10, and then the VBE of Q1 and Q2 is adjusted by Q3 to Q6. (ON) Voltage, thereby enabling the regulation of the oscillation frequency.

[0047] In some embodiments, the oscillation main circuit includes resistors R5~R6, transistors Q1~Q6, capacitor C, and current sources I1~I6, wherein:

[0048] The input terminal of current source I1 is connected to the power supply voltage, and the output terminal of current source I1 is connected to the collector of transistor Q8.

[0049] The output terminals of current sources I2~I6 are grounded. The input terminal of current source I2 is connected to the emitter of transistor Q3 and the base of transistor Q2. The connection point between the base of transistor Q2 and the input terminal of current source I2 is the first output terminal of the differential cross-coupled multivibrator. The input terminal of current source I3 is connected to the emitter of transistor Q1 and one end of capacitor C. The input terminal of current source I4 is connected to the emitter of transistor Q7. The input terminal of current source I5 is connected to the emitter of transistor Q2 and the other end of capacitor C. The input terminal of current source I6 is connected to the emitter of transistor Q4 and the base of transistor Q1. The connection point between the base of transistor Q1 and the input terminal of current source I6 is the second output terminal of the differential cross-coupled multivibrator.

[0050] The collector of transistor Q1 is connected to the base of transistor Q3, the emitter of transistor Q5, and one end of resistor R5, with the other end of resistor R5 connected to the power supply voltage; the collector of transistor Q3 is connected to the power supply voltage, and the base and collector of transistor Q5 are connected to the emitter of transistor Q9; the collector of transistor Q2 is connected to the base of transistor Q4, the emitter of transistor Q6, and one end of resistor R6, with the other end of resistor R6 connected to the power supply voltage; the collector of transistor Q4 is connected to the power supply voltage, and the base and collector of transistor Q6 are connected to the emitter of transistor Q10.

[0051] In some embodiments, the resistance values ​​of resistors R5 to R6 are the same, and the currents of current sources I1 to I6 are the same.

[0052] In some embodiments, transistors Q7 and Q10 are NPN transistors, and transistors Q8 and Q9 are PNP transistors.

[0053] In some embodiments, transistors Q1 to Q6 are NPN transistors.

[0054] The working principle of the differential cross-coupled multivibrator proposed in this invention is as follows: the initial control voltage value Vin is transmitted to V1 through a control voltage selection circuit. V1 is first decreased and then increased by one VBE via Q7 and Q9, and then increased and then decreased by one VBE via Q8 and Q10, finally reaching V2, making V2 equal to V1. Subsequently, the branches containing Q1 and Q2 alternately charge and discharge capacitor C, thereby generating an oscillation signal output.

[0055] In some embodiments, a simulation experiment is performed on the circuit proposed in this invention. With switches S0, S1, and S2 all disconnected, the constructed circuit is simulated and verified. The simulation output waveform is as follows: Figure 4 As shown. Simulation results show that the oscillator works normally and can generate a good square wave signal with an amplitude of approximately twice the VBE voltage. Under the condition of a fixed initial input control voltage Vin, switches S0, S1, and S2 are closed respectively to obtain different actual control voltages, and the circuit is simulated and verified. The results are shown below. Figure 5 As shown in the figure. Simulation results show that the output frequency changes accordingly with the actual control voltage. The oscillator in this invention achieves adjustable resonant frequency.

[0056] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "rotation," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0057] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A differential cross-coupled multivibrator, characterized in that, include: The main oscillation circuit is used to generate periodic rectangular waves; A control voltage selection circuit is used to adjust the frequency of the oscillation main circuit by selecting a control voltage. The control voltage buffer circuit is used to suppress power supply noise interference in the main oscillation circuit and assists the control voltage selection circuit in achieving frequency regulation.

2. The differential cross-coupled multivibrator according to claim 1, characterized in that, The control voltage selection circuit includes switches S1~S3, resistors R1~R4, and capacitor C1, wherein: One end of resistor R1 is connected to voltage Vin, and the other end of resistor R1 is connected to one end of resistor R2; the other end of resistor R2 is connected to one end of resistor R3, the other end of resistor R3 is connected to resistor R4, and the other end of resistor R4 is grounded. Switch S1 is connected across resistor R2, switch S2 is connected across resistor R3, and switch S3 is connected across resistor R4. One end of the capacitor is connected to one end of the resistor R2 and the control voltage buffer circuit; the other end of the capacitor C1 is grounded.

3. A differential cross-coupled multivibrator according to claim 2, characterized in that, Resistors R2 to R4 have the same resistance value, and the resistance value of resistor R1 is twice that of resistor R2.

4. A differential cross-coupled multivibrator according to claim 2, characterized in that, The control voltage buffer circuit includes transistors Q7~Q10, wherein: The bases of transistors Q7 to Q8 are connected to capacitor C1 in the control voltage selection circuit, and the connection point is denoted as V1. The collector of transistor Q7 is connected to the power supply voltage, and the emitter of transistor Q7 is connected to the base of transistor Q9 and the main oscillation circuit. The collector of transistor Q9 is grounded, and the emitter of transistor Q9 is connected to the emitter of transistor Q10, and the connection point is denoted as V2. The emitters of transistors Q9 to Q10 are also connected to the main oscillation circuit. The collector of transistor Q8 is grounded. The emitter of transistor Q8 is connected to the main oscillation circuit, as well as the base and collector of transistor Q10. The collector of transistor Q10 is connected to the power supply voltage.

5. A differential cross-coupled multivibrator according to claim 4, characterized in that, Transistors Q7 and Q10 are NPN transistors, while transistors Q8 and Q9 are PNP transistors.

6. A differential cross-coupled multivibrator according to claim 1 or 4, characterized in that, The main oscillation circuit includes resistors R5~R6, transistors Q1~Q6, capacitor C, and current sources I1~I6, wherein: The input terminal of current source I1 is connected to the power supply voltage, and the output terminal of current source I1 is connected to the collector of transistor Q8. The output terminals of current sources I2~I6 are grounded. The input terminal of current source I2 is connected to the emitter of transistor Q3 and the base of transistor Q2. The connection point between the base of transistor Q2 and the input terminal of current source I2 is the first output terminal of the differential cross-coupled multivibrator. The input terminal of current source I3 is connected to the emitter of transistor Q1 and one end of capacitor C. The input terminal of current source I4 is connected to the emitter of transistor Q7. The input terminal of current source I5 is connected to the emitter of transistor Q2 and the other end of capacitor C. The input terminal of current source I6 is connected to the emitter of transistor Q4 and the base of transistor Q1. The connection point between the base of transistor Q1 and the input terminal of current source I6 is the second output terminal of the differential cross-coupled multivibrator. The collector of transistor Q1 is connected to the base of transistor Q3, the emitter of transistor Q5, and one end of resistor R5, with the other end of resistor R5 connected to the power supply voltage; the collector of transistor Q3 is connected to the power supply voltage, and the base and collector of transistor Q5 are connected to the emitter of transistor Q9; the collector of transistor Q2 is connected to the base of transistor Q4, the emitter of transistor Q6, and one end of resistor R6, with the other end of resistor R6 connected to the power supply voltage; the collector of transistor Q4 is connected to the power supply voltage, and the base and collector of transistor Q6 are connected to the emitter of transistor Q10.

7. A differential cross-coupled multivibrator according to claim 6, characterized in that, The resistors R5 to R6 have the same resistance value, and the current sources I1 to I6 have the same current.

8. A differential cross-coupled multivibrator according to claim 6, characterized in that, Transistors Q1 to Q6 are NPN transistors.

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