A New Differential Crystal Oscillator Circuit
By using bipolar transistors in the differential crystal oscillator circuit and adding auxiliary vibration start circuit, the vibration start and phase noise problems of traditional differential crystal oscillators are solved, and better stability and noise performance are achieved.
Patent Information
- Application Number
- CN202210587463.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-05-27
- Publication Date
- 2025-03-18
- Estimated Expiration
- 2042-05-27
AI Technical Summary
When using bipolar transistors, traditional differential crystal oscillators are prone to cause vibration problems under mismatch conditions, and due to the flickering noise of the metal field effect tube, the output phase noise is poor.
A new differential crystal oscillator circuit was designed, using bipolar transistors as gain tubes, and the vibration problem was solved by adding auxiliary vibration start circuits, including low-resistance paths and field effect transistors.
It effectively reduces the phase noise at the output terminal, avoids the start-up problem of bipolar transistors under mismatch conditions, and improves the stability of the oscillator.
Smart Images
Figure CN114900130B_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of electronic circuit design technology, and in particular relates to a novel differential crystal oscillator circuit. Background Art
[0002] In wireless communication systems, oscillators are a very critical part and are often used to generate reference frequencies. Therefore, the frequency needs to be adjustable within a certain range while maintaining good stability. LC oscillators can achieve frequency adjustment, but the generated frequency stability is poor. Therefore, in wireless communication systems, crystal oscillators are often used to generate frequencies with good stability. Crystals, such as quartz, often have a higher Q value, making it easier to generate stable frequencies.
[0003] For different transceivers, the harmonics of the oscillator can easily couple to other RF circuits through multiple paths and appear at the output. Compared with the single-ended structure, the differential crystal oscillator has better immunity to various interferences.
[0004] In traditional common differential crystal oscillator circuits, metal field effect transistors are often used as gain tubes. Since the gate of the metal field effect tube has no current path, the structure formed by the two gain tubes in the oscillator will not cause startup problems due to mismatch. However, metal field effect tubes have large flicker noise, which is more obvious at lower frequencies. Therefore, this structure greatly deteriorates the proximal phase noise, resulting in poor output phase noise of the oscillator. In order to solve the problem of poor output noise, bipolar transistors are often used in traditional differential crystal oscillator circuits. However, current flows through the gate of the bipolar transistor. In differential mode, the two bipolar transistors form a latch in the oscillator circuit. Under mismatch conditions, they are easily locked in another abnormal state due to the positive feedback effect, which will cause startup problems. Summary of the invention
[0005] Purpose of the invention: In order to solve the noise problem of the traditional differential crystal oscillator and the oscillation starting problem introduced thereby, the present invention proposes a novel differential crystal oscillator circuit.
[0006] Technical solution: The present invention discloses a novel differential crystal oscillator circuit, comprising an oscillator, a first load, a second load, a fifth resistor, a sixth resistor, a first bipolar transistor, a second bipolar transistor and a low-resistance path for assisting the oscillator in starting;
[0007] One end of the oscillator is connected to the collector of the first bipolar transistor, the collector of the first bipolar transistor is simultaneously connected to an external power supply through a first load, and the collector of the first bipolar transistor is connected to the base of the second bipolar transistor, and the emitter of the first bipolar transistor is grounded;
[0008] The other end of the oscillator is connected to the collector of the second bipolar transistor, the collector of the second bipolar transistor is simultaneously connected to the external power supply through the second load, and the collector of the second bipolar transistor is connected to the base of the first bipolar transistor, and the emitter of the second bipolar transistor is grounded;
[0009] One end of the low-resistance path is connected to the differential output end of the oscillator, the other end of the low-resistance path is connected to the base of the first bipolar transistor through a fifth resistor, and the other end of the low-resistance path is connected to the base of the second bipolar transistor through a sixth resistor.
[0010] Further, the low resistance path includes a third resistor, a fourth resistor, a first field effect transistor and a second field effect transistor;
[0011] The third resistor and the fourth resistor are connected in series, and then connected to the differential output terminal of the oscillator, the gate of the first field effect transistor is connected to the connection point between the third resistor and the fourth resistor, the drain of the first field effect transistor is connected to the external power supply, the source of the first field effect transistor is connected to the drain of the second field effect transistor, the source of the first field effect transistor is connected to the gate of the second field effect transistor, and the source of the second field effect transistor is grounded;
[0012] The base of the first bipolar transistor is connected to the gate of the second field effect transistor through a fifth resistor; the base of the second bipolar transistor is connected to the gate of the second field effect transistor through a sixth resistor.
[0013] Further, the first load is a first resistor, and the second load is a second resistor.
[0014] Furthermore, the first load is a first current source, and the second load is a second current source.
[0015] Furthermore, the first field effect transistor may be replaced by a third bipolar transistor.
[0016] Furthermore, the second field effect transistor may be replaced by a fourth bipolar transistor.
[0017] Beneficial effects: The present invention solves the oscillation problem of bipolar transistors under mismatch conditions by adding an auxiliary oscillation circuit, and the present invention greatly reduces the phase noise at the output end by using bipolar transistors as gain tubes in a differential crystal oscillator circuit. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 This is a new differential crystal oscillator circuit diagram using resistance as load;
[0019] Figure 2 This is a new differential crystal oscillator circuit diagram that uses a current source as a load.
[0020] Figure 3 This is a new differential crystal oscillator circuit diagram that uses a field effect tube as a load.
[0021] Figure 4 This is a new differential crystal oscillator circuit diagram that uses inductance as load. DETAILED DESCRIPTION
[0022] The technical solution of the present invention is now further described in conjunction with the accompanying drawings.
[0023] A novel differential crystal oscillator circuit of the present invention mainly includes: an oscillator X1, a first load, a second load, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a first bipolar transistor M1, a second bipolar transistor M2, a first field effect transistor M3 and a second field effect transistor M4.
[0024] One end of the oscillator X1 is connected to the collector of the first bipolar transistor M1, the collector of the first bipolar transistor M1 is connected to the external power supply through the first load, and the collector of the first bipolar transistor M1 is connected to the base of the second bipolar transistor M2. The emitter of the first bipolar transistor M1 is grounded.
[0025] The other end of the oscillator X1 is connected to the collector of the second bipolar transistor M2, the collector of the second bipolar transistor M2 is connected to the external power supply through the second load, and the collector of the second bipolar transistor M2 is connected to the base of the first bipolar transistor M1. The emitter of the second bipolar transistor M2 is grounded.
[0026] The third resistor R3, the fourth resistor R4, the first field effect transistor M3 and the second field effect transistor M4 constitute an oscillation auxiliary circuit, whose main function is: by introducing a low-resistance path at low frequency, the loop gain of the two bipolar transistors at low frequency is low, which solves the oscillation problem of the bipolar transistors M1 and M2 under mismatch conditions. The specific circuit structure of the oscillation auxiliary circuit is further described. The third resistor R3 is connected in series with the fourth resistor R4, and then connected in parallel with the oscillator X1. The gate of the first field effect transistor M3 is connected to the connection point between the third resistor R3 and the fourth resistor R4, the drain of the first field effect transistor M3 is connected to an external power supply, the source of the first field effect transistor M3 is connected to the drain of the second field effect transistor M4, and is also connected to the gate of the second field effect transistor M4, and the source of the second field effect transistor M4 is grounded.
[0027] The base of the first bipolar transistor M1 is connected to the gate of the second field effect transistor M4 through the fifth resistor R5; the base of the second bipolar transistor M1 is connected to the gate of the second field effect transistor M4 through the sixth resistor R6.
[0028] The present invention adopts bipolar transistors M1 and M2 as gain tubes. Since bipolar transistors have no flicker noise, the phase noise at the output end of the crystal oscillator circuit is greatly improved.
[0029] like Figure 1 As shown, a resistor can be used as a load, that is, a new differential crystal oscillator circuit, which mainly includes: an oscillator X1, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a first bipolar transistor M1, a second bipolar transistor M2, a first field effect transistor M3 and a second field effect transistor M4.
[0030] One end of the oscillator X1 is connected to the collector of the first bipolar transistor M1, the collector of the first bipolar transistor M1 is connected to the external power supply through the first resistor R1, and the collector of the first bipolar transistor M1 is connected to the base of the second bipolar transistor M2. The emitter of the first bipolar transistor M1 is grounded.
[0031] The other end of the oscillator X1 is connected to the collector of the second bipolar transistor M2, the collector of the second bipolar transistor M2 is connected to the external power supply through the second resistor R2, and the collector of the second bipolar transistor M2 is connected to the base of the first bipolar transistor M1. The emitter of the second bipolar transistor M2 is grounded.
[0032] The third resistor R3, the fourth resistor R4, the first field effect transistor M3 and the second field effect transistor M4 form a low resistance path for assisting oscillation.
[0033] like Figure 2 As shown, a current source can be used as a load, that is, a new differential crystal oscillator circuit, which mainly includes: an oscillator X1, a first current source I1, a second current source I2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a first bipolar transistor M1, a second bipolar transistor M2, a first field effect transistor M3 and a second field effect transistor M4.
[0034] One end of the oscillator X1 is connected to the collector of the first bipolar transistor M1, the collector of the first bipolar transistor M1 is connected to the external power supply through the first current source I1, and the collector of the first bipolar transistor M1 is connected to the base of the second bipolar transistor M2. The emitter of the first bipolar transistor M1 is grounded.
[0035] The other end of the oscillator X1 is connected to the collector of the second bipolar transistor M2, the collector of the second bipolar transistor M2 is connected to the external power supply through the second current source I2, and the collector of the second bipolar transistor M2 is connected to the base of the first bipolar transistor M1. The emitter of the second bipolar transistor M2 is grounded.
[0036] The third resistor R3, the fourth resistor R4, the first field effect transistor M3 and the second field effect transistor M4 form a low resistance path for assisting oscillation.
[0037] The first field effect transistor M3 and the second field effect transistor M4 may be replaced by bipolar transistors, or one of them may be a bipolar transistor and the other may be a field effect transistor.
[0038] The structure of the auxiliary circuit may also be a circuit structure with a similar principle.
Claims
1. A novel differential crystal oscillator circuit, characterized in that: It includes an oscillator, a first load, a second load, a fifth resistor, a sixth resistor, a first bipolar transistor, a second bipolar transistor and a low-resistance path for assisting the oscillator in starting up; One end of the oscillator is connected to the collector of the first bipolar transistor, the collector of the first bipolar transistor is simultaneously connected to an external power supply through a first load, and the collector of the first bipolar transistor is connected to the base of the second bipolar transistor, and the emitter of the first bipolar transistor is grounded; The other end of the oscillator is connected to the collector of the second bipolar transistor, the collector of the second bipolar transistor is simultaneously connected to the external power supply through the second load, and the collector of the second bipolar transistor is connected to the base of the first bipolar transistor, and the emitter of the second bipolar transistor is grounded; One end of the low-resistance path is connected to the differential output end of the oscillator, the other end of the low-resistance path is connected to the base of the first bipolar transistor through a fifth resistor, and the other end of the low-resistance path is connected to the base of the second bipolar transistor through a sixth resistor; The low resistance path includes a third resistor, a fourth resistor, a first field effect transistor and a second field effect transistor; The third resistor and the fourth resistor are connected in series, and then connected to the differential output terminal of the oscillator, the gate of the first field effect transistor is connected to the connection point between the third resistor and the fourth resistor, the drain of the first field effect transistor is connected to the external power supply, the source of the first field effect transistor is connected to the drain of the second field effect transistor, the source of the first field effect transistor is connected to the gate of the second field effect transistor, and the source of the second field effect transistor is grounded; The base of the first bipolar transistor is connected to the gate of the second field effect transistor through a fifth resistor; the base of the second bipolar transistor is connected to the gate of the second field effect transistor through a sixth resistor.
2. A novel differential crystal oscillator circuit according to claim 1, characterized in that: The first load is a first resistor, and the second load is a second resistor.
3. A novel differential crystal oscillator circuit according to claim 1, characterized in that: The first load is a first current source, and the second load is a second current source.
4. A novel differential crystal oscillator circuit according to claim 1, characterized in that: The first field effect transistor may be replaced by a third bipolar transistor.
5. A novel differential crystal oscillator circuit according to claim 1 or 4, characterized in that: The second field effect transistor may be replaced by a fourth bipolar transistor.
Citation Information
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