Ask a question
Can I turn the RF source on or off within 200 ns?
In pulse radar systems, high power amplifiers (HPAs) need to switch on and off rapidly during the transition from transmit to receive mode. The typical target for this switching time is less than 1 μs. Traditionally, this has been achieved using drain control, which involves switching large currents between 28 V and 50 V. While switching power technology can handle this, it introduces additional size and complexity into the design. In modern phased array antenna systems, where size, weight, and power (SWaP) are critical, there's a growing need to simplify these processes and eliminate the complexity of drain switches.
This article presents a novel and straightforward gate pulse drive circuit that offers a fast HPA switching solution without the need for traditional drain switches. The measured switching time is under 200 ns, providing more than enough margin for applications requiring less than 1 μs. Additional features include programmable offset adjustment to account for device-to-device variations, gate clamping to prevent voltage spikes, and overshoot compensation to improve pulse rise time.
A typical drain pulse configuration uses a series FET to control the HPA’s drain voltage. The control circuit must convert a logic-level signal into a higher voltage to activate the FET. However, this approach requires careful management of inductance, charge storage, and timing to avoid conflicts. It also often involves an N-channel FET, which requires a higher voltage than the drain to turn on, adding further complexity.
To address these challenges, a gate drive circuit is proposed. This circuit converts a logic-level input into a controlled negative voltage signal suitable for GaN HPA gate control. It ensures fast rise times, minimal overshoot, and stable biasing. A rail-to-rail operational amplifier with high slew rate is ideal for this task, as it can quickly respond to changes in the input signal.
The recommended gate pulse circuit shown in Figure 2 uses an op-amp in an inverting configuration with a precision DAC to set the reference voltage. When the logic input is low, the output is at a small negative voltage, effectively turning the HPA on. When the input is high, the op-amp is clamped to the negative supply rail, turning the HPA off. Components such as resistors and capacitors are chosen to optimize performance, including noise filtering, clamping, and pulse shaping.
Testing was conducted using evaluation boards for the DAC, op-amp, and HPA. A pulse generator simulated a 1.8 V logic signal, and the HPA’s response was measured using an RF sampling oscilloscope. The results showed that the HPA turned on in less than 200 ns and turned off even faster, both well within the 1 μs target.
Layout considerations were also explored, showing that the circuit can be implemented in a compact form suitable for high-density phased array systems. With minimal additional space required, this design is ideal for future integrated radar systems.
In conclusion, this gate pulse circuit provides a reliable, fast, and compact alternative to traditional drain control methods. It supports fast HPA switching, eliminates device variation issues through programmable offsets, and includes protective features like gate clamping. As electronic systems become more integrated, this approach is expected to gain traction in phased array applications requiring rapid RF source control.
Large Event Combination Speaker,Lightweight Combo Speaker,Professional Stage Subwoofer Speaker,Vc60.6Mm Performance Speaker
NINGBO RFUN AUDIO TECHNOLOGY CO.,LTD , https://www.mosensound.com