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Mar 5 2019

Crystal Oscillator Circuit Diagram (Ten Kinds of Crystal Oscillator Circuit Diagrams)

Warm hints: This article contains about 2500 words and reading time is about 15 mins.

Introduction

The crystal oscillator refers to a slice (abbreviated as a wafer) from a quartz crystal at a certain azimuth angle, a quartz crystal resonator, which is simply referred to as a quartz crystal or a crystal, a crystal oscillator; and a crystal element in which an IC constitutes an oscillation circuit is added inside the package is called Crystal oscillator. Its products are typically packaged in a metal case and are also available in glass, ceramic or plastic.

Article Core

Crystal oscillator

Purpose

Introduce ten kinds of crystal oscillator circuit diagrams.

Application

Semiconductor industry.

Keywords

Crystal oscillator

Catalog

Introduction


Crystal Oscillator Circuit Diagram (1)


Crystal Oscillator Circuit Diagram (2)

1. Component Selection

2. Notice

Crystal Oscillator Circuit Diagram (3)


Crystal Oscillator Circuit Diagram (4)


Crystal Oscillator Circuit Diagram (5)


Crystal Oscillator Circuit Diagram (6)


Crystal Oscillator Circuit Diagram (7)


Crystal Oscillator Circuit Diagram (8)


Crystal Oscillator Circuit Diagram (9)


Crystal Oscillator Circuit Diagram (10)



Crystal Oscillator Circuit Diagram (1)

As shown in the figure, it is a simple crystal oscillator circuit composed of three gates of A1, four resistors, tuning capacitors and a crystal. In the figure, A1 and the crystal resonator SJT and the capacitor constitute a square wave signal of 4069 kHz. Set the switch to 1 point and send it to A2. After A2 is divided by two, the 2048kHz oscillation signal is obtained. The switch is placed at 3 points and sent to A3. After A2 is divided by two, the 128kHz oscillation signal is obtained. Tuning capacitors C1 and C2 allows the frequency to be accurately tuned to the center frequency. The crystal SJT is connected between the input and output terminals of A1 to provide a feedback loop at the fundamental frequency of the crystal.

In the figure, A1 and the crystal resonator SJT and the capacitor constitute a square wave signal of 4069 kHz. Set the switch to 1 point and send it to A2. After A2 is divided by two, the 2048kHz oscillation signal is obtained. The switch is placed at 3 points and sent to A3. After A2 is divided by two, the 128kHz oscillation signal is obtained. Tuning capacitors C1 and C2 allows the frequency to be accurately tuned to the center frequency.

Crystal Oscillator Circuit Diagram (1)

The crystal SJT is connected between the input and output terminals of A1 to provide a feedback loop that produces oscillations at the fundamental frequency of the crystal.


Crystal Oscillator Circuit Diagram (2)

The pole tube TV2 performs signal amplification and is coupled out through the capacitor C8. Among them, the resistors RI, R2 and the resistors R5, R6, and R7 are DC biasing elements of the transistors VT1 and VT2. L2 is a high frequency choke coil that provides a DC path to the collector current of the oscillating tube VT1. C2 is a DC blocking capacitor. C3 and C7 are AC bypass capacitors, so that the emitter of VT1 is at AC zero potential, but the DC potential is not zero. Inductor L1, capacitor C6, and resistor R3 are improved power supply filter circuits, which function to reduce the ripple voltage to oscillate the DC component. The capacitors C4 and C8 can be slightly adjusted to change the size of the coupled signal.

Crystal Oscillator Circuit Diagram (2)


1. Component Selection

Capacitor C1 is 20p, C2 is 100p, C3 and C7 are 820p, C4 is 56p, C5 and C8 are 47p, and C6 is 47u/50V. The inductance L1 is 22 uH (color code inductance), and L2 is 0.3 uH. Resistor R1 is 1.6kΩ, R2 is 1kΩ, R3 is 750Ω, R4 is 180Ω, 1W, R5 is 1.3kΩ, R6 is 3kΩ, R7 is 360Ω, R8 is 470Ω, and R9-R12 is 300Ω, 2W. Transistor VT1, VT2 select 3DG82B, 65 ≤ β ≤ 115. The crystal SJT uses JA9B type -70MHz. The relay KM is JUC-1M.

2. Notice

(1) When applying quartz crystals, there is a practical problem that must be noted. This is the excitation power of the crystal itself. When the excitation power is large, the output power is also large. At this time, the noise introduced by the transistor is not greatly affected. However, excessive crystal excitation power deteriorates the long-term stability (aging characteristics) of the crystal. When the crystal excitation power is small, the long-term stability is good, but it is preferable to use a low-noise crystal triode.

(2) Since the crystal frequency is greatly affected by temperature, in order to ensure the stability of the crystal frequency, it is necessary to pay attention to the crystal constant temperature. The crystal is placed in a constant temperature bath, and the temperature in the constant temperature bath is maintained by the constant temperature control circuit to maintain the inflection point temperature of the crystal. Therefore, in order to stabilize the oscillation frequency and the oscillation amplitude, the crystals SJT and VT1, VT2 are placed in the incubator. The incubator is heated by R9-R12 four 2W metal film resistors, and a small sealed temperature relay KM is used as a temperature control element. The temperature inside the box is +55 ° C (the inflection point temperature of the crystal used is generally +60 ± 5 ° C). In order to reduce the volume of the incubator, the components in the circuit should be as small as possible. If the temperature inside the box is higher than +55 °C, the KM-1.2 contact is disconnected; if ≤ +55 °C, the KM-1.2 contact is closed to ensure that the temperature inside the box is set at +55 °C.


Crystal Oscillator Circuit Diagram (3)

Crystal Oscillator Circuit Diagram (3)

The circuit oscillates in the frequency range from 100kHz to 5MHz. The operating characteristics are determined by the source resistance. The frequency can be adjusted using a trimmer capacitor. The output resistance is high, followed by a source follower as an isolator to support this shortcoming.


Crystal Oscillator Circuit Diagram (4)

This simple and inexpensive crystal oscillator consists of two gates and peripheral components of the 74LS04. The circuit is shown in Figure 3:

Crystal Oscillator Circuit Diagram (4)

Resistors R1 and R2 bias the two inverters F1, F2 in a linear range and provide a feedback loop from the crystal SJT, which produces a 20MHz oscillation frequency at the fundamental frequency of the crystal, which is then sent by inverter F3 to 74LS74. The constructed D-type flip-flop is divided. To perform two-way or four-way, eight-way, etc., you need to follow the 2n frequency division rule (n is the number of stages). n=1, then 21=2 frequency division, that is, 20MHz after A1=frequency dividing circuit, Q1 output 10MHz; if four frequency division, n=2, then 22=4 frequency division, that is, 20MHz is divided by A1 and A2 After the circuit, Q2 outputs 5MHz; if the frequency is divided by three, when the third pulse of f is over, Q1=1, Q2=1, then Q1=0, Q2=0, or the output of the non-gate HF1 is 1, to The R terminal resets, and Q1 and Q2 are reset to 00. After the A1 and A2 are divided by three, the Q2 output is about 6.7MHz. If the frequency is divided by five, when the count is 5, Q1Q2Q3=101, that is, Q1=0. Q3=0, the output of the NOR gate HF2 is 1, and Q1, Q2, and Q3 are reset to 000. As a result, Q3 outputs a 4MHz frequency.

It is clear that the output state is determined by D, and the flipping of the output state is controlled by the CP, which can generate a variety of frequencies suitable for their needs.


Crystal Oscillator Circuit Diagram (5)

Crystal Oscillator Circuit Diagram (5)

A crystal oscillator circuit using an operational amplifier. This circuit uses a 761 operational amplifier with an output pulse frequency of up to 10MHz. The 2kΩ resistor is used as the open collector load for the op amp output stage.


Crystal Oscillator Circuit Diagram (6)

Crystal Oscillator Circuit Diagram (6)

Radio radio circuit with quartz crystal oscillator. This circuit frequency can be 27MHz. The intermediate frequency is 455 kHz. In order to increase the received power, a field effect transistor pre-stage is used here.


Crystal Oscillator Circuit Diagram (7)

Quartz crystal oscillator circuit with frequency up to 2MHz.

Crystal Oscillator Circuit Diagram (7)

Figures (a) and (b) show two 2MHz oscillator basic circuits. According to the circuit structure, the optimum operating point can be determined through test adjustment.


Crystal Oscillator Circuit Diagram (8)

Field Effect Crystal Glimpse Quartz Crystal Oscillator Circuit

Crystal Oscillator Circuit Diagram (8)

The oscillator operates with a 51MHz (17MHz 3rd harmonic) crystal. Depending on the structure, the drain-to-gate capacitance can be selected from 0.5 to 1.8 pF. The L2 parameter is approximately 20% of L1. The oscillation characteristics can be changed by a 470Ω source resistance.


Crystal Oscillator Circuit Diagram (9)

30MHs quartz crystal oscillator circuit using NAND gate

Crystal Oscillator Circuit Diagram (9)

This circuit consists of a TTL integrated circuit (745000). Use the 3rd harmonic operation of the quartz crystal frequency. Oscillation performance is guaranteed by the precise selection of 47pF capacitors (10-100pF). The output voltage is approximately 3.5V (peak-to-peak).


Crystal Oscillator Circuit Diagram (10)

Quartz crystal oscillator circuit using NAND gate

Crystal Oscillator Circuit Diagram (10)

The circuit uses two 7400TTL NAND gates with an oscillating frequency of up to 10MHz. The two 820Ω resistors must be carefully tuned to the selected oscillation frequency.


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