The heart of the circuit consists of a Hartly oscillator, Q1. To reduce loading, a 10kΩ resistor couples the source output of Q1 to the high input impedance gate of source follower JFET Q2. Q2 then drives BJT emitter follower Q3, which in turn drives BJT amplifier Q4. A toroidal core transformer, T1, couples the output of Q4 to a 50Ω load to provide 2.61Vp-p or 12.3 dBm. Spice circuit simulations predict a second harmonic with an amplitude 35dB below the fundamental. The second harmonic amplitude exceeds all higher harmonic amplitudes, and oscilloscope measurements show a clean-looking sine wave across the 50Ω load.
To provide a good termination for the amplifier and still get 7.3 dBm (1.47 Vp-p), for example, to drive a diode ring mixer, you can insert a 50Ω 5dB spacer between the output transformer T1 and the load. Resistor R2 is used to adjust the RF output level, and for improved stability, you can also replace R2 with a fixed resistor divider consisting of low temperature coefficient metal film fixed resistors. Part of the signal at the collector of Q4 drives the gate of the JFET source follower Q5 through C7 and R9. Diode D1 rectifies the signal, which is filtered and input to the inverting input of op amp IC1. Resistor R1 and low temperature coefficient potentiometer R2 shunt the 12V supply to provide a DC reference voltage to the positive input of IC1 and set the level of the input signal. After filtering, the DC output of IC1 drives the gate 2 of Q1 to set the gain of the device and control the RF output.
The frequency of the oscillator can be precisely adjusted using trimmer capacitor C18 connected to the center tap of coil L1. If the reduction in frequency stability is acceptable, C18 can be replaced with a low-cost ceramic trimmer. Piston-type trimmers are quite expensive and not as readily available as ceramic trimmers, but typical ceramic trimmers exhibit temperature coefficients at least an order of magnitude worse than piston-type trimmers. To operate the oscillator at frequencies other than 18 MHz, increase the inductance of L1 along with C12, C13, C16, C17, and C18 by a factor of 18/fOSC2. Where fOSC2 is the new frequency in MHz. Adjust the tap on the source connection of Q1 to keep it at approximately 20% of the total number of turns from the ground end of the inductor.
You can replace the series capacitor bank consisting of C12 and C13 with a 13pF capacitor, and C14 and C15 with a 2.5pF capacitor. If you want to redesign the circuit for a different output frequency, adjust the capacitance values of C14 and C15, or their individual replacements, to get enough capacitance to ensure reliable startup under all expected operating conditions. Note, however, that using two capacitors, C16 and C17, helps reduce startup drift, as does using temperature-stable (NP0 characteristics) ceramic dielectric capacitors for C12 to C17. Buffer amplifiers Q2 to Q4 need to be modified to operate above approximately 25 MHz.
A well-regulated external DC power supply (not shown) provides 12V, -12V, and 8V to the circuit. To maintain high stability and keep Q1's maximum drain-source voltage specification of 12V, the oscillator can only use an 8V supply. At a constant ambient temperature of 22°C and using specified components, the average drift rate of the oscillator frequency is -2 to -3 Hz per minute over 1 hour after an initial 10-minute warm-up.
Previous article:MAX1084/MAX1085 Serial 10-Bit ADCs with Internal Voltage Reference
Next article:MAX9263, MAX9264 Gigabit Multimedia Serial-Link Serializers/Deserializers
- Popular Resources
- Popular amplifiers
- Signal Integrity and Power Integrity Analysis (Eric Bogatin)
- Detailed circuit introduction of commonly used operational amplifiers.doc
- Wireless Communication Electronics:Introduction to RF Circuits and Design...
- Introduction to the classification, application, composition and model of phase-locked loop
- High signal-to-noise ratio MEMS microphone drives artificial intelligence interaction
- Advantages of using a differential-to-single-ended RF amplifier in a transmit signal chain design
- ON Semiconductor CEO Appears at Munich Electronica Show and Launches Treo Platform
- ON Semiconductor Launches Industry-Leading Analog and Mixed-Signal Platform
- Analog Devices ADAQ7767-1 μModule DAQ Solution for Rapid Development of Precision Data Acquisition Systems Now Available at Mouser
- Domestic high-precision, high-speed ADC chips are on the rise
- Microcontrollers that combine Hi-Fi, intelligence and USB multi-channel features – ushering in a new era of digital audio
- Using capacitive PGA, Naxin Micro launches high-precision multi-channel 24/16-bit Δ-Σ ADC
- Fully Differential Amplifier Provides High Voltage, Low Noise Signals for Precision Data Acquisition Signal Chain
- Innolux's intelligent steer-by-wire solution makes cars smarter and safer
- 8051 MCU - Parity Check
- How to efficiently balance the sensitivity of tactile sensing interfaces
- What should I do if the servo motor shakes? What causes the servo motor to shake quickly?
- 【Brushless Motor】Analysis of three-phase BLDC motor and sharing of two popular development boards
- Midea Industrial Technology's subsidiaries Clou Electronics and Hekang New Energy jointly appeared at the Munich Battery Energy Storage Exhibition and Solar Energy Exhibition
- Guoxin Sichen | Application of ferroelectric memory PB85RS2MC in power battery management, with a capacity of 2M
- Analysis of common faults of frequency converter
- In a head-on competition with Qualcomm, what kind of cockpit products has Intel come up with?
- Dalian Rongke's all-vanadium liquid flow battery energy storage equipment industrialization project has entered the sprint stage before production
- Allegro MicroSystems Introduces Advanced Magnetic and Inductive Position Sensing Solutions at Electronica 2024
- Car key in the left hand, liveness detection radar in the right hand, UWB is imperative for cars!
- After a decade of rapid development, domestic CIS has entered the market
- Aegis Dagger Battery + Thor EM-i Super Hybrid, Geely New Energy has thrown out two "king bombs"
- A brief discussion on functional safety - fault, error, and failure
- In the smart car 2.0 cycle, these core industry chains are facing major opportunities!
- The United States and Japan are developing new batteries. CATL faces challenges? How should China's new energy battery industry respond?
- Murata launches high-precision 6-axis inertial sensor for automobiles
- Ford patents pre-charge alarm to help save costs and respond to emergencies
- New real-time microcontroller system from Texas Instruments enables smarter processing in automotive and industrial applications
- EEWORLD University ---- TINA-TI (TM) series courses
- Moto 360 Wireless Charging Base Disassembly
- What is MU-MIMO and why is it important for Wi-Fi 6 and 6E?
- 【Lazy Self-Care Fish Tank Control System】Work Submission
- [Summer benefits to celebrate the Dragon Boat Festival] A large number of technical information is waiting for you to claim, and there are also gifts to help
- Please help me find which resistor in the picture is the 1.1K resistor in the formula?
- Xiaozhi Science Popularization丨How to Correctly Understand Power Supply Ripple and Noise
- Find the maximum voltage stress of the diode when it is working
- About QQ Chat at Work
- Naming method of TMS320 chip