It is difficult to get noise free signal in microwave frequency range of 30 gigahertz and above, Fujitsu has announced millimeter wave low noise signal generator circuit for automotive radar and other millimeter-band RF transceiver. The specialty of this innovation is this circuit can be used to produce IC chips with this function using silicon semiconductor material.
The low-noise signal-generating circuit from Fujitsu consists of multiple comparators for operating sequential comparisons to reference signal to reduce unwanted noise in the millimeter-band signal by 5 dB.
Details on this technology was presented at the European Microwave Integrated Circuits Conference 2013 (EuMIC 2013), which held on October 6 in Germany.
Though it is easy to achieve this performance on compound semiconductor material based chips, but they are expensive. Fujitsu able to achieve in fabricating this circuit using silicon.
Fujitsu has given the below explanation on how its multiple phase circuit improves the noise performance of 30 GHz+ signal generator:
Present technology: Millimeter-band transceiver ICs need a signal-generating circuit to generate millimeter-band signals. Conventional millimeter-band signal-generating circuits compare the low frequency comparator signals, which are divided from the frequency of millimeter-band oscillator signals, to the low-noise, highly stable reference signals from the reference oscillator. They then synchronize these two signals to generate low-noise, highly stable signals . Because the reference signal and comparator signal share the same frequency and a comparison is made one time for each cycle of the reference signal, the phase difference signal of the comparison results cannot be made sufficiently large compared to the noise generated from the phase difference detection circuits, and results in the problem of high levels of noise. In particular, because the level of noise generated by the transistors made of silicon semiconductors is high compared to that of compound semiconductors, there has been a need for circuit technology that generates low-noise and highly stable millimeter-band signals.
About the New Technology
Fujitsu's improvement: The newly developed technology employs a new architecture in which multiple phase difference detection circuits and delay circuits are connected in a line, enabling multiple comparisons to be made. In the new circuit, the frequency of the comparison signal is raised and, furthermore, the reference signal is split into multiple signals, enabling multiple comparisons per cycle. A phase difference signal is generated from each comparison, and because there are now more differential signals, their relative size, in relation to the noise generated by the phase difference detection circuit, is now larger, thereby enabling a reduction in the impact of the generated noise. Signal noise was successfully reduced by 5 dB below previous levels, resulting in approximately just one-third of the previous noise level.
In applying these technologies, Fujitsu plans to develop a single-chip millimeter-band transceiver IC module.