Automotive Radars have introduced various functions on automobiles for driver’s safety and comfort, as part of the Intelligent Transportation System (ITS) including Adaptive Cruise Control (ACC), collision warning or avoidance, blind spot surveillance and parking assistance.
Although such radar systems with 24 GHz carrier frequency are already in use but due to some regulatory issues, recently a permanent band has been allocated at 77-81 GHz, allowing for long-term development of the radar service. In fact, switchover to the new band is mandatory by 2014.
A frequency multiplier will be one of the key components for such a millimeter wave automotive radar system because there are limitations in direct implementation of low phase noise oscillators at high frequencies. A practical way to build a cost-effective and stable source at higher frequency is to use an active multiplier preceded by a high spectral purity VCO operating at a lower frequency. Recent improvements in the performance of SiGe technology allow the silicon microelectronics to advance into areas previously restricted to compound semiconductor devices and make it a strong competitor for automotive radar applications at 79 GHz.
This study presents the design of active frequency doubler circuits at 20 GHz in a commercially available SiGe BiCMOS technology and at 40GHz in SiGe bipolar technology (Infineon-B7h200 design). Buffer/amplifier circuits are included at output stages to drive 50 Ω load. The frequency doubler at 20 GHz is based on an emitter-coupled pair operating in class-B configuration at 1.8 V supply voltage. Pre-layout simulations show its conversion gain of 10 dB at -5 dBm input, fundamental suppression of 25dB and NF of 12dB. Input and output impedance matching networks are designed to match 50 Ω at both sides.
The millimeter wave frequency doubler is designed for 5 V supply voltage and has the Gilbert cell-based differential architecture where both RF and LO ports are tied together to act as a frequency doubler. Both pre-layout and post-layout simulation results are presented and compared together. The extracted circuit has a conversion gain of 8 dB at -8 dB input, fundamental suppression of 20 dB, NF of 12 dB and it consumes 42 mA current from supply. The layout occupies an area of 0.12 mm2 without pads and baluns at both input and output ports. The frequency multiplier circuits have been designed using Cadence Design Tool.
Source: Linköping University
Author: Altaf, Amjad