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The Right Mix: RF Switches Adopt the GaN Recipe

This fabless semiconductor company is showing how gallium-nitride technology can be employed to develop high-power RF switches without the need to stack devices.

Utilization of gallium nitride (GaN) in the RF/microwave industry has soared in recent years, with the technology now playing a key role in applications across the board. GaN and amplifiers seem to go hand-in-hand, as companies are capitalizing on the benefits of GaN technology to develop the latest and greatest high-power amplifiers.

But one firm, Tagore Technology, is exploiting GaN for use cases beyond high-power amplifiers. Specifically, Tagore Technology is touting its family of GaN-based RF switches, which the company maintains offers several advantages in comparison to alternative solutions.

Tagore Technology, located in Arlington Heights, Ill., is a fabless semiconductor company founded in January of 2011. With more than 50 customers worldwide, the company targets applications that range from cellular infrastructure to land-mobile radios (LMRs). Furthermore, Tagore Technology is not only invested in RF switches, but is using GaN technology to develop RF power transistors as well as power-management solutions.

What’s the reasoning behind developing RF switches based on GaN technology? Manish Shah, VP of engineering at Tagore Technology, explains, “There are two key requirements for RF devices used in RF switch circuits. The ‘OFF’ arm devices need to handle very large voltages under high-RF-power conditions, while the ‘ON’ arm devices need to handle high currents. For example, 10 W of RF power in a perfectly matched 50-Ω condition will create a peak RF voltage of 32 V and a peak current of 600 mA. A voltage standing wave ratio (VSWR) of 4:1, which is very typical for RF switches close to the antenna, would push that voltage to 51 V and the current to 1 A.”

Shah continues, “Existing technologies, such as SOI/SOS/GaAs with a breakdown voltage around 3 V, would require stacking of a prohibitively large number of devices to handle such a large voltage. PIN-diode-based switches achieve this by reverse-biasing the diode with very large voltages to keep them ‘OFF’ and large currents to achieve low RDS(on) during the ‘ON’ state.”

Shah points out that GaN technology is well-suited for the design of high-power RF switches. “Wide-bandgap GaN HEMT has very high breakdown voltage capability,” he says. “The saturation current of GaN is also very high; it’s typically in the range of 800 to 900 mA/mm. So high-power switches designed using GaN devices can meet high voltage and high current requirements without stacking devices. Unlike a PIN diode, the GaN HEMT is a voltage-controlled device. Thus, it doesn’t require high current during the ‘ON’ state. This makes GaN an ideal technology for high-power RF switch design.”

Getting to Know the Products

Tagore Technology was on hand at IMS 2019, showcasing its RF switches and other devices (Fig. 1). The company’s complete portfolio of switches covers frequencies that range from 1 MHz to 6 GHz.

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1. On display at IMS 2019 was Tagore Technology’s family of GaN-based RF switches.

One example is the TS7226K symmetrical single-pole, double-throw (SPDT) switch. Covering a frequency range of 500 MHz to 6 GHz, the TS7226K is intended for broadband, high-peak-power switching applications. At 2,600 MHz, the switch has a specified 0.1-dB compression point of +42.5 dBm under continuous-wave (CW) operating conditions. Under pulsed conditions (1% duty cycle and 10-µs frame width), the TS7226K can handle peak power levels as high as +48 dBm. The device comes in a 3- × 3-mm quad-flat no-leads (QFN) package.

Then there’s the TS7329K, a 100-W asymmetrical SPDT switch that covers a frequency range of 700 MHz to 5 GHz. Like the TS7226K, the TS7329K comes in a 3- × 3-mm QFN package.

As mentioned earlier, Tagore also offers RF power transistors, which were on display at IMS, too (Fig. 2). One product is the TA8110K 4-W GaN-on-silicon (GaN-on-Si) power transistor that covers a frequency range of 30 MHz to 2.7 GHz. This device is intended to be used as a driver for high-power-amplifier applications. The TA8110K also comes in a 3- × 3-mm QFN package.

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2. Among the products available from Tagore are RF power transistors like the TA8110K and TA8210D.

Also offered by Tagore is the TA8210D 12.5-W GaN-on-Si power transistor that covers a frequency range of 20 MHz to 3 GHz. The TA8210D will find homes in LMR/PMR/MIL radios.

Speaking of LMR/PMR/MIL radios, Tagore Technology is leveraging its switch technology to enhance the performance of multiband power amplifiers (PAs) for these applications. The company has developed proprietary low-impedance switches, which can be placed at the output of the PA. Each individual output switch path can then be matched, resulting in much higher efficiencies for multiband PA applications. (For more on this, Tagore published an application note titled “Application Board Using TA8210D + SP4T switch.”)

Tagore Technology’s future plans include products such as low-noise amplifiers (LNAs).

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