System simulations of a 1.5 V SiGe 81–86 GHz E-band transmitter
Analog Integrated Circuits and Signal Processing
This paper presents simulation results for a sliding-IF SiGe E-band transmitter circuit for the 81-86 GHz E-band. The circuit was designed in a SiGe process with f T = 200 GHz and uses a supply of 1.5 V. The low supply voltage eliminates the need for a dedicated transmitter voltage regulator. The carrier generation is based on a 28 GHz quadrature voltage oscillator (QVCO). Upconversion to 84 GHz is performed by first mixing with the QVCO signals, converting the signal from baseband to 28 GHz,
... d then mixing it with the 56 GHz QVCO second harmonic, present at the emitter nodes of the QVCO core devices. The second mixer is connected to a threestage power amplifier utilizing capacitive cross-coupling to increase the gain, providing a saturated output power of ?14 dBm with a 1 dB output compression point of ?11 dBm. E-band radio links using higher order modulation, e.g. 64 QAM, are sensitive to I/Q phase errors. The presented design is based on a 28 GHz QVCO, the lower frequency reducing the phase error due to mismatch in active and passive devices. The I/Q mismatch can be further reduced by adjusting varactors connected to each QVCO output. The analog performance of the transmitter is based on ADS Momentum models of all inductors and transformers, and layout parasitic extracted views of the active parts. For the simulations with a 16 QAM modulated baseband input signal, however, the Momentum models were replaced with lumped equivalent models to ease simulator convergence. Constellation diagrams and error vector magnitude (EVM) were calculated in MATLAB using data from transient simulations. The EVM dependency on QVCO phase noise, I/Q imbalance and PA compression has been analyzed. For an average output power of 7.5 dBm, the design achieves 7.2% EVM for a 16 QAM signal with 1 GHz bandwidth. The current consumption of the transmitter, including the PA, equals 131 mA from a 1.5 V supply.