RF Amplifier’s Input Power Over-Drive Switch NEW VERSION

50 Ohms in/out SMA ports
HMC784 RF Switch
1 MHZ – >1 GHZ
-30…..+40 dBm RF power input – 10 Watts max
30 dB isolation if the input power exceeds the preset threshold
12 W / 50 Ohm load resistor to dissipate the input power
Several requests have been received regarding the availability of a reliable solution for protecting high-cost RF power LDMOS transistors, which can be easily damaged by excessive input drive levels.

This is a wideband protection solution (LF to >1 GHz)as a solution for protection high-cost RF power LDMOS transistors, which can be easily damaged by excessive input drive levels. Under normal operating conditions, the input signal is routed directly to the output connector and experiences only the insertion loss of the RF switch, which is approximately 0.15 dB at 30 MHz and remains below 1 dB up to 1 GHz.

The input signal is continuously monitored using a logarithmic amplifier circuit based on the Analog Devices ADL5513, offering extremely fast response comparable to that of a diode detector. As long as the detected signal level remains below a user-defined threshold, the RF switch maintains the direct signal path from input to output with minimal loss. When the input power exceeds the preset threshold, a voltage comparator activates the RF switch, diverting the input signal to a resistive termination consisting of four 200 Ω / 3 W resistors configured as a 50 Ω dummy load.

This action effectively protects the input of the downstream amplifier by providing isolation through the RF switch. Typical isolation is approximately 20 dB at higher frequencies and significantly greater at lower frequencies, reaching 35 to 75 dB across the HF and VHF ranges. The protection remains active for as long as the input power exceeds the threshold. Once the input level falls below the threshold, the RF switch automatically reconnects the signal path to the output port.

The device is suitable not only for protecting RF power amplifier inputs, but also for safeguarding receiver inputs, spectrum analyzer inputs, and SDR front-ends from overdrive and potential damage.

The latest revision of the RF Power Overdrive Protection Switch module requires only a single +12 V DC supply at approximately 50 mA. All additional voltage rails are generated on-board using integrated voltage regulators.

An LED drive output (LD2) is provided for connection of an external indicator LED, offering visual indication of an overdrive condition if required.

Additional applications include use as a modulator, limiter, or clipping device, among others.

PCB dimensions: 47 × 53 mm