Effect of idler terminations on the conversion loss for THz Schottky diode harmonic mixers

Abstract

Efficient and reliable frequency converters, preferably operating at room temperature, are critical components for frequency-stabilizing terahertz sources. In this work, we present the analysis of optimum configurations for Schottky diode based x4, x6, and x8 harmonic mixers operating at 2.3 THz, 3.5 THz, and 4.7 THz respectively. Detailed large-signal analysis of the two basic single-ended Z-and Y-mixers was carried out using a standard Schottkydiode model. For each case, the conversion loss was minimized by finding optimal embedding impedances at RF, LO, and IF frequencies. The analysis shows that the Y-mixer has less conversion loss at a low LO pump power. However, the Zmixer provides reduced loss with increasing harmonic index and pump power due to the associated power dissipation in idler circuits. The results provide preliminary design guidelines for room-temperature frequency converters and their use in phase-locked loop applications.

A 3.5-THz, ×6-Harmonic, Single-Ended Schottky Diode Mixer for Frequency Stabilization of Quantum-Cascade Lasers

“…The embedding impedances of a Schottky diode with a sub-micron anode area were evaluated using a large-signal, harmonic-balance simulation. Using the built-in optimizer in the circuit simulator, the diode-embedding impedances at the RF, IF, and LO frequency were varied to provide a low mixer conversion loss L. The out-of-band frequencies were terminated by an open circuit (Z-mixer topology) [22], [23]. The RF optimum diode-embedding impedance of the Z-mixer is approximately Z RF = (60 + j80) Ω as shown in Fig.…”

“…3. At the LO and IF the optimum impedances are approximately Z LO = (150 + j300) Ω and 1000 Ω respectively [23]. The predicted conversion loss L from the ideal Z-mixer circuit simulation was about 20 dB for a Schottky contact area of 0.11 µm 2 , an LO power = 2 dBm, no dc bias, and the losses from the mixer circuit were excluded.…”

A 3.5-THz, x6-Harmonic, Single-Ended Schottky Diode Mixer for Frequency Stabilization of Quantum-Cascade Lasers

“…The embedding impedances of a Schottky diode with a sub-micron anode area were evaluated using a large-signal, harmonic-balance simulation. Using the built-in optimizer in the circuit simulator, the diode-embedding impedances at the RF, IF, and LO frequency were varied to provide a low mixer conversion loss L. The out-of-band frequencies were terminated by an open circuit (Z-mixer topology) [19], [20]. The RF optimum diode-embedding impedance of the Z-mixer is approximately Z RF = (60 + j80) Ω as shown in Fig.…”