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10 to 1000 MHz Oscillator Schematic Circuit Diagram

Modernizing Oscillator Design with Integrated VCO ICs

Building oscillators no longer requires assembling discrete components. Manufacturers now offer pre-made Voltage-Controlled Oscillator (VCO) Integrated Circuits (ICs) that only necessitate a few external components to determine frequency. One such example is the RF Micro Devices RF2506. Operating within a supply voltage range of 2.7 to 3.6 V (with a nominal voltage of 3.3 V). This IC features a low-noise oscillator transistor with an integrated DC bias setting. Additionally, it incorporates an isolating buffer amplifier that effectively mitigates the impact of load variations (load pulling) on the oscillator.

Efficient Control and Operation

When a voltage lower than 0.7 V is applied to the power-down input (pin 8), the oscillator deactivates, reducing the current consumption from 9 mA to less than 1 µA. The VCO activates when the voltage on pin 8 reaches at least +3.0 V. By connecting the feedback capacitors C1 and C2 to pins 3 (FDBK) and 4 (VTUNE). The internal transistor transforms into a Colpitts oscillator.

Optimizing Resonance and Tunability

To complete the oscillator setup, a resonator comprising C4 and L1, coupled via C3, is required. Maintaining a high Q factor for the coil (perhaps by utilizing an air-core coil) ensures minimal phase noise. Most applications demand a tunable oscillator. The varicap diode D1 (such as BBY40, BBY51, BB804, etc.) can be employed to adjust the resonant frequency. The tuning voltage, UTune, is applied through a high resistance with a specific value depending on the desired frequency range and the chosen variable-capacitance diode (D1).

10 to 1000 MHz Oscillator Schematic Circuit Diagram 1

Guidelines for Frequency-Determining Components

The provided table offers several recommendations for choosing frequency-determining components. For narrow frequency ranges, it’s advisable to connect a parallel-resonant circuit between the output pin and +Vcc. This setup serves as the collector load for the output transistor and can be constructed using the same components as the oscillator resonator.

Broadband VCO Configuration

In the case of a broadband Voltage-Controlled Oscillator (VCO), opt for an HF choke instead. Its value should range from a few microhenries to a few nanohenries, depending on the desired frequency band. Here, C6 becomes unnecessary. With an LC load, this circuit produces an output level of –3 dBm, whereas with a choke load, it delivers –7 dBm. The accompanying schematic diagram includes a table outlining approximate component values for various frequencies, serving as a starting point for experimentation.

10 to 1000 MHz Oscillator Schematic Table

The coupling between the variable-capacitance diode and C5 determines the tuning range of the VCO. The manufacturer maintains an Internet site at, where you can find more information about this interesting oscillator IC.


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