Fully Integrated Digital GaN-Based LSK Demodulator for High-Temperature Applications

Abstract

We present the first Gallium Nitride (GaN)-based demodulator system dedicated to demodulating Load-Shift Keying (LSK) modulated signals that can operate at high temperature (HT). GaN500 technology is adopted to implement the proposed demodulator. Stable DC output characteristics of epitaxial AlGaN/GaN Heterojunction Field Effect Transistors (HFETs) operating at up to 500 o C enable designing HT ICs. Conventional digital gates such as inverters, NAND2, NAND3, delay elements and a D Flip-Flop are employed to implement the proposed demodulator. The demodulation system is fabricated on a 2.67 mm 2 silicon carbide (SiC) substrate and experimentally validated at 160 o C, whereas the building blocks (inverters and NANDs) show a stable operation at HT up to 400 o C. A minimum of 1 V amplitude difference can be detected between the high voltage level (HVL = ± 5 V) and low voltage level (LVL = ± 4 V) of an applied LSK modulated signal to recover transmitted digital data. Two high-voltage supply levels (±14 V) are required to operate the system. Its total power consumption is 3.4 W.

Circuit Techniques in GaN Technology for High-Temperature Environments

“…This modulation system was based on a simplified delta-sigma modulation technique, and a fully digital demodulator was implemented to recover data from a modulated signal. The reported simulation results confirmed the functionality of the proposed systems over temperatures ranging from 25 • C to 350 • C. The digital demodulator was experimentally validated in [18] at 160 • C. In [19], we performed the HT characterization and modeling of GaN500 devices showing a stable operation up to 600 • C. The characterization results were used to extract an extended version of the Angelov model of GaN HFETs after considering the temperature as a variable parameter.…”

“…Recently, we had investigated the possibility of using GaN500 HEMT technology to implement HT ICs [15][16][17][18][19] at the Polystim Laboratory [20]. The results reported in [15] confirmed the stability of tested GaN devices from room temperature up to 400 • C. In [16], basic digital circuits were implemented using GaN500 and off-chip resistors achieving HT operation up to 400 • C. In addition, three demodulators were demonstrated to recover data from an LSK-based modulated signal.…”

“…The test chip was wire bonded to a ceramic package that can endure the HT inside the furnace. The measurement setup is shown in Figure 2 and more details about the HT packaging and testing setup can be found in [18].…”

“…However, the pads were limited to control all circuits. INV4: This inverter is used along with INV3 in the digital demodulator system [18]. The schematics of INV4 is shown in Figure 9d, and its micrograph is presented in Figure 10d.…”

“…The micrograph of the D Flip-Flop is presented in Figure 25b and the transient response is shown in Figure 27 at 25, 100, and 160 • C. Similar to the Delay circuit, after 160 • C the D Flip-Flop stops working due to shifts of inputs and outputs levels of the NANDs. More details could be found in [18].…”