PLL Oscillator for Medium Wave Application Circuit

PLL oscillator is used to get very stable frequency woth very low distortion of sine wave output. The stability is equal to crystal-based oscillator, and the low distortion level of the sine wave output is equal to LC based oscillator. The method of PLL control in PLL oscillator is done by adjusting the frequency of sine wave VCO (voltage controlled oscillaltor). The VCO is an LC based oscillator, but the capacitor is not a fixed one, but it’s a varactor, a variable capacitor which its capacitance value is variable depends on the applied voltage. 

The control of this voltage change the frequency of the VCO. This voltage control is coming from a phase difference detector that detect the phase difference between the crystal reference clock and the VCO output. If the frequency of the VCO output is different then the error signal from the phase difference detector will try to correct the VCO until the VCO has the same frequency and the phase difference is slipped at certain level to produce the voltage control that maintain the VCO frequency.

Multiplying PLL Oscillator’s Output Frequency

To get the frequency higher than the PLL oscillator’s internal reference clock, we just need to insert a frequency divider between the VCO and the phase difference detector. Using this method, now the PLL control system will maintain the divided VCO output frequency to be same with the reference, so the PLL Oscillator that come directly from the VCO has the frequency of the reference frequency multiplied by the division value of the programmed divider. 

PLL Oscillator Circuit

This is the figure of the oscillator circuit;

Simple PLL oscillator circuit can be constructed using MC145106 IC, and it need only external VCO to produce a sine wave output. The crystal frequency is 4608 kHz for European medium wave frequency spacing standart, and 5120 for USA. The power supply must be regulated and well decoupled.

555 Timer Voltage Controlled Oscillator Circuit

This is a circuit of a voltage-controlled oscillator (VCO) that uses the 555 timer IC as the main component. As expected, the 555 timer is configured as an astable multi vibrator to be able to serve as an oscillator. An astable multi vibrator is just a timing circuit whose output oscillates between 'low' and 'high' continuously, in effect generating a train of pulses. This is the figure of the circuit;

The difference of this circuit with the basic 555 astable circuit is that its 555's pin 5 is tied to an external voltage source.  Pin 5 is the 555's control voltage pin, which allows the user to directly adjust the threshold voltages to which the pin 2/pin 6 input voltages are compared by the 555's internal comparators.  Since the outputs of these comparators control the internal flip-flop that toggles the output of the 555, adjusting the pin 5 control voltage also adjusts the frequency at which the 555 toggles its output. Increasing the input voltage at pin 5 decreases the output oscillation frequency while decreasing the input voltage increases the output oscillation frequency.

Low Distortion Crystal Oscillator Circuit

This is a design circuit for Low Distortion Crystal Oscillator circuit. This circuit generate a sine wave that has low phase noise and distortion. This circuit can be used to perform a crystal with less than 1mV dissipated in crystal. The crystal is used to filter the signal current. This is the figure of the circuit;

 

If the impedance loads is low, the JFET will drive the impedance. When the loads is about 50ohm, it will better if an emitter follower combined with a voltage step-down transformer or matching network for further buffering. The value of C3 determined the output voltage, if the lower output voltage is required, the C3′s value should be increased and decrease the value of C3 when the larger output voltage is needed. If overtone crystal is used, a choke should replace the 1K emitter resistor. This choke must be resonates with C2 at a frequency slightly above the fundamental frequency for third overtone crystals. When uses the high-Q overtone crystal, the value of C3 should be lower because the High-Q overtone crystals should be driven at much lower levels than  fundamental  crystals. Besides that, the output level should be set as low as possible. If the crystal’s rated  power or current is  known, the drive level can be measured. To measure drive level temporarily connect a 100 ohm across C3 and measure the signal level on the source of the FET. The crystal current is determined by V/100.

UJT Relaxation Oscillator with Op-Amp Squarer

The UJT below is configured to produce a sawtooth wave at a frequency of 104 Hz. The capacitor begins to charge through the 4.7 kOhm resistor when the circuit is initially powered up. The current suddenly flows from the UJT emitter (E) to the UJT Base (B1) when the voltage across the capacitor rises to a certain point. This will produce a voltage across the 100 ohm resistor which is the same as the output of the UJT relaxation oscillator on the Emitter. This is the figure of the circuit;

The sawtooth waveform is applied to op amp pin 3 and the voltage divider is applied to op amp 2. The op amp produces a positive going output on [in 6 when the sawtooth is higher than the reference from the divider of 2.5 volts. The op amp acts as a comparator. [Circuit's schematic diagram source: Chuck Bolin Electronic Project].

Decibel Sound Pressure Level Meter Circuit

This is a design for decibel meter circuit. This circuit is used to measure sound pressure level (SPL) from about 60 to 70 dB. In this circuit, the transistor stage and one LM324 op-amp section are used to amplify the sound that is picked up by an 8 ohm speaker. As voltage comparators, the circuit uses The remaining 3 sections of the LM324 quad op-amp. 3 indicator LEDs are driven by the LM324. This is the figure of the circuit;


This circuit uses 3 LEDs as indicators. Each LED represents about a 3dB change in sound level, so that when all 3 LEDs are on, the sound level is about 4 times greater than the level needed to light one LED. the 500K pot can be used to adjust the sensitivity of the circuit. One LED is used as a reference sound level. The other two LEDs is used to indicate about a 2X and 4X increase in volume.

Wien Bridge Oscillator Using CA3140

This is a bridge oscillator circuit. This circuit is excellent use of its high input impedance, high slew rate, and high voltage qualities and it is called the Wien Bridge sine wave oscillator. This is the figure of the circuit.


Oscillator stabilization takes on many forms. It must be precisely set, otherwise the amplitude will either diminish or reach some form of limiting with high levels of distortion. The element, RS, is commonly replaced with some variable resistance element. Thus, through some control means, the value of RS is adjusted to maintain constant oscillator output. A FET channel resistance, a thermistor, a lamp bulb, or other device whose resistance increases as the output amplitude is increased are a few of the elements often utilized. As the output signal amplitude increases, the zener diode impedance decreases resulting in more feedback with consequent reduction in gain; thus stabilizing the amplitude of the output signal. [Project Schematic source: Intersil Corporation].

Wien Bridge Oscillator Circuit

This is a circuit that is known as wien bridge oscillator circuit. The circuit has positive and negative feedback loop. This circuit is work with control by op amp. This is the figure of the circuit.


The circuit oscillates at a frequency determined by the RC time constant at frequency and produces a sinusoidal waveform at the output voltage Vout. In many cases this circuit is used as sine wave generator which is using rail to rail op amp. [Schematic’s diagram source: Advanced Linear Devices, Inc]

Tuned Sine Wave Oscillator Circuit With Op Amp

This is a design circuit for sine wave oscillators that will provide both a sine and square wave output for frequencies from below 20 Hz to above 20 KHz. The frequency of oscillation is easily tuned by varying a single resistor. This circuit is controlled by two op amp, LM111 and LM101A. This is the figure of the circuit.


In this circuit, an operational amplifier has function as a tuned circuit, driven by square wave from a voltage comparator. The frequency is controlled by R1, R2, C1, C2, and R3, with R3 used for tuning. Tuning the filter does not affect its gain or bandwidth so the output amplitude does not change with frequency. A comparator is fed with the sine wave output to obtain a square wave. The square wave is then fed back to the input of the tuned circuit to cause oscillation. Zener diode, D1, stabilizes the amplitude of the square wave fed back to the filter input. Starting is insured by R6 and C5 which provide dc negative feedback around the comparator. This keeps the comparator in the active region. [Schematic diagram source: National Semiconductor. Inc]

Phase Shift Oscillator Circuit

This is a design circuit of a simple inexpensive amplitude stabilized phase shift sine wave oscillator which requires one IC package, three transistors and runs off a single supply. This circuit is combination with the RC network comprises a phase shift configuration and oscillates at about 12 kHz. The remaining circuitry provides amplitude stability. Here’s the schematic figure of the circuit.


The high impedance output at Q2's collector is fed to the input of the LM386 via the 10 μF-1M series network. This circuit is using op amp LM386 causes it has fixed gain of 20. The 1M resistor in combination with the internal 50 kΩ unit in the LM386 divides Q2's output by 20. The positive peaks at the amplifier output are rectified and stored in the 5 μF capacitor. This potential is fed to the base of Q3. Q3's collector current will vary with the difference between its base and emitter voltages. Since the emitter voltage is fixed by the LM313 1.2V reference, Q3 performs a comparison function and its collector current modulates Q1's base voltage. Q1, an emitter follower, provides servo controlled drive to the Q2 oscillator.a

Low Distortion Sine Wave Oscillator

One approach to generating sine waves is to filter a square wave. This leaves only the sine wave fundamental as the output. Since a square wave is easily amplitude stabilized by clipping, the sine wave output is also amplitude stabilized. For the solution of the problem, you can look at the figure below.


A lower distortion oscillator is needed. It can be used. Instead of driving the tuned circuit with a square wave, a symmetrically clipped sine wave is used. The clipped sine wave, of course, has less distortion than a square wave and yields a low distortion output when filtered. This circuit is not as tolerant of component values as tune sine wave oscillator. To insure oscillation, it is necessary that sufficient signal is applied to the zener for clipping to occur.

Clipping about 20% of the sine wave is usually a good value. The level of clipping must be high enough to insure oscillation over the entire tuning range. If the clipping is too small, it is possible for the circuit to cease oscillation due to tuning, component aging, or temperature changes. Higher clipping levels increase distortion. [Schematic’s diagram source: National Semiconductor. Inc]

Colpitts Crystal Oscillator Circuit

This is a design schematic of a Crystal Colpitts oscillator can be implemented using a transistor and a parallel mode crystal. This is the figure of the circuit.


In this circuit, the crystal is use as an inductance. A large value capacitive divider is used between gate, source, and ground, and a small series capacitor is placed in the crystal circuit. You should choose the components values so that C2+C3 to C1 ratio has the highest possible value. The ratio of 5 to 10 to 1 is usually used. The schematic shows the typical values. This circuit introduce is a little loading on the crystal. The relatively high value is of C2 and C3 “swamp out” variations and drift caused by variations in device characteristics. Frequency can be fine tuned with C1. A clean enough sine wave appears at the emitter of the transistor.