A DC-to-170GHz Direct-Coupled Mixer Achieving 47dB LO-RF Isolation in 250nm InP DHBT Technology

A DC-to-170-GHz down-conversion mixer was fabricated in 250-nm InP DHBT technology for VNAs. The chip is direct coupled, which integrates LO and RF baluns, a Gilbert mixer cell, and IF amplifiers. Three successive differential pairs are employed at the LO port to reshape the LO input signal three times, thereby improving the balance of the balun and enhancing the LO-to-RF isolation to 47 dB. Couplers, bypass capacitors, radial stub capacitors, and microstrip lines are employed in the mixer cell to extend the bandwidth. The mixer is capable of operating in both <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\times 1$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\times 3$</tex> LO mixing modes with 0-dBm LO power. For the fundamental LO (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\times 1$</tex>) mixer measurements, the MMIC achieves a conversion loss of 9 dB and an input <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{1\text{dB}}$</tex> of 5 dBm at DC-67 GHz. For the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\times 3$</tex> harmonic mixer measurements, it achieves a conversion loss of 22 dB and an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{P}_{1\text{dB}}$</tex> of 0 dBm at 67-170 GHz.