Proliferation of 2.4-GHz Communications Systems
The 2.4-GHz ISM (Industrial, Scientific, and Medical) band has witnessed a surge in the number of communication systems operating within it. Bluetooth, various WLAN (Wireless Local Area Network), and Home-RF systems are just a few examples of technologies utilizing this frequency range. As a result, the need for a straightforward test oscillator operating between 2.4 GHz and 2.5 GHz has become paramount, especially for testing receivers in these systems.
Integrated Test Oscillator: Maxim’s Solution
Maxim offers a convenient solution in the form of a single IC, the MAX2750, available at www.maxim-ic.com. This integrated circuit covers the frequency range from 2.4 GHz to 2.5 GHz by utilizing an internal LC network, which can be tuned with an embedded varactor diode. The IC includes an output buffer delivering a power level of –3 dBm into a 50 Ω load. Housed within an 8-pin µMAX package, it simplifies the process of testing receivers within the specified frequency band.
Powering and Stabilizing the Circuit
The circuit operates on a 9-V battery. To stabilize the battery voltage around 4 V, a BC238C transistor is employed. Although the MAX2750 can function with supply voltages ranging from +2.7 V to +5.5 V, employing a stabilized supply voltage enhances the free-running oscillator’s frequency stability. All connections to the IC are decoupled using 220pF capacitors, positioned as close to the IC pins as feasible. The tuning voltage at pin 2, TUNE, can be adjusted between +0.4 V and +2.4 V, offering a tuning range spanning from 2.4 GHz to 2.5 GHz.
Oscillator Control and Output Level Adjustment
To deactivate the oscillator, connecting the Shutdown input (SHDN) to ground effectively shuts down the IC, reducing its current consumption to approximately 1 µA. In the given configuration, the shutdown input is linked to the Vcc potential through a pull-up resistor, ensuring continuous oscillator operation. Additionally, the –3 dB output level can be attenuated further using the specified pi attenuator.
Understanding Wireless Local Area Networks (WLANs)
Wireless LANs, commonly referred to as WLANs, are wireless computer networks linking multiple devices via wireless communication within confined areas like homes, schools, offices, or campuses. Utilizing high-frequency radio waves, WLANs often incorporate an access point for Internet connectivity. One of their key advantages is that they enable users to maintain network connections while moving within the coverage area, enhancing mobility and flexibility within home or office spaces.
