HMC735LP5E

The HMC735LP5E is a high-performance monolithic microwave integrated circuit (MMIC) voltage controlled oscillator (VCO) from Analog Devices Hittite microwave product line. Fabricated using GaAs InGaP heterojunction bipolar transistor (HBT) technology, this X-band VCO covers a frequency range of 10.5 to 12.2 GHz with a tuning voltage range of 1V to 15V. What sets the HMC735LP5E apart from discrete VCO solutions is its complete monolithic integration: all critical components including the resonator, negative resistance active devices, varactor diodes, and output buffer amplifiers are fabricated on a single GaAs die. This monolithic construction delivers several key advantages: exceptional phase noise performance that remains consistent over temperature, mechanical shock, and process variations; no external resonator components required; and minimal frequency pulling due to load impedance changes. The VCO provides two output signals: the main RF output at the fundamental frequency (Fo = 10.5-12.2 GHz) delivering +17 dBm typical output power, and a divide-by-4 output (Fo/4 = 2.625-3.05 GHz) that is ideal for use as a PLL feedback signal or as a lower frequency reference output. The prescaler can be disabled when not needed, reducing total supply current by approximately 100 mA for power-sensitive applications. The main output buffer provides excellent load pulling performance of only 50 MHz peak-to-peak into a 2:1 VSWR, ensuring frequency stability even when driving mismatched loads. The HMC735LP5E operates from a single +5V supply with a typical total supply current of 180 mA (217 mA max). Housed in a compact 32-lead 5×5 mm QFN package with an exposed thermal pad for efficient heat dissipation, the device requires no external matching components, significantly simplifying board design and reducing overall solution footprint. The E suffix version is RoHS compliant with 100% matte tin lead finish and MSL3 rating.

The HMC735LP5E is a voltage controlled oscillator based on a negative-resistance topology implemented in GaAs InGaP HBT technology. The core of the VCO consists of a pair of HBT transistors configured in a cross-coupled or Colpitts-style negative resistance configuration that compensates for the losses in the resonant tank circuit. The resonant tank is formed by integrated transmission line resonators and varactor diodes. The varactor diodes are semiconductor devices whose capacitance varies with applied reverse bias voltage – as the tuning voltage (VTUNE) increases, the varactor capacitance decreases, raising the resonant frequency of the tank circuit, and vice versa. This voltage-dependent tuning allows the oscillator frequency to be electronically controlled over the 10.5 to 12.2 GHz range. The negative resistance from the active devices cancels the equivalent parallel resistance of the tank, sustaining oscillation at the resonant frequency. Since all resonator elements are monolithically integrated on the same GaAs substrate, the VCO exhibits excellent phase noise and frequency stability – there are no external components to introduce noise or mechanical instability. The oscillator signal is buffered by an amplifier stage that provides isolation between the VCO core and the load, minimizing frequency pulling effects caused by load impedance variations. This buffer also delivers the +17 dBm output power. A separate divide-by-4 prescaler circuit takes a portion of the main VCO signal and divides it by four, producing a lower frequency output at Fo/4. This divider is implemented with digital logic and can be powered down by leaving the Vcc(Dig) pin open, saving approximately 100 mA of supply current. The divide-by-4 output is particularly useful in PLL applications as it provides a lower frequency signal that can be directly compared with a reference frequency in a phase-frequency detector, eliminating the need for an external prescaler. The thermal management is handled through the exposed ground paddle on the bottom of the QFN package, which must be soldered to the PCB ground plane to provide both a low-inductance RF ground and a low-thermal-resistance path for heat dissipation.

• Point-to-point and point-to-multipoint microwave backhaul radios
• Local oscillator (LO) for X-band upconverters and downconverters
• SATCOM and VSAT satellite ground station equipment
• Test and measurement: signal generators, spectrum analyzers, network analyzers
• Military radar and electronic warfare (EW) systems
• Phased array antenna beam steering systems (used in ADI CN0566 reference design)
• PLL frequency synthesizers with external PLL IC (e.g., ADF4159)
• Industrial microwave sensors and radar level measurement
• Aerospace and defense communication systems
• Broadband communication infrastructure equipment