Efficient, Switching-Free Buck and Boost Conversion for RF Circuits

Published in the September 2026 issue of Microwave Journal, this feature article introduces the Enhanced Linear Regulator (ELR) to the RF and microwave design community. Next-generation RF systems need voltage regulators that are small, efficient, and quiet at once, and conventional parts force a three-way trade-off: switching regulators are efficient but generate conducted and radiated EMI; linear regulators (LDOs) are clean but waste power as heat on any sizeable voltage step and can only step down; and the usual workaround, a switching regulator followed by an LDO, inflates the bill of materials, footprint, and thermal design. The ELR co-packages a silicon LDO with GaAs photovoltaic-output optocouplers that convert power a linear regulator would dissipate into useful output power. With optocoupler efficiencies above 52%, ELR bucks reach 60 to 90% efficiency depending on step size, and the same photovoltaic devices enable purely linear, ripple-free boost conversion.

The article describes the BK300D50E, developed for a 12 V or higher input stepping down to 5 V or less with extremely low output noise. Five series-connected GaAs optocouplers, each generating roughly 1 V at maximum power, are co-packaged with an Analog Devices LT3045 LDO in a 7 mm × 7 mm QFN32 package; the LT3045's power-good, current-limit, and enable functions are retained, and a BYP pin bypasses the LED array so the device can run as a conventional LDO. Measured at 13 V in, 5 V out, and 100 mA load, its input current is dramatically lower than an LT3045 alone over the same step. Output noise stays below 1 µVRMS with spot noise of about 2 nV/√Hz at 10 kHz, and power-supply ripple rejection exceeds 120 dB, including more than 75 dB at 1 MHz.

The design-in is a voltage-variable attenuator (VVA) from Planar Monolithics (PMI). At 60 dB of attenuation and beyond, a switching regulator's ripple and harmonics appear as discrete spurs above the attenuated signal, so the supply, not the attenuator, sets the achievable dynamic range. The incumbent switching regulator at 15 V input drew at most 115 mA yet left spurs on the RF carrier; an all-linear supply removed them at 300 mA and excessive heat; and a switcher-plus-LDO stage carried a prohibitive footprint while still leaving spurs incompatible with a 100 dB dynamic-range target. The BK300D50E eliminated the switching spurs while drawing 165 mA, near-switching-level efficiency, and spectrum-analyzer measurements of the RF carrier show a dynamic-range improvement of more than 30 dB. Because the ELR follows standard LDO design practice, it also removes the EMC design work that accompanies a switching regulator and significantly reduces the power-management bill of materials.