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The key issue is a synthesized LO generator with excellent phase noise close to the carrier and much improved phase noise at offset frequencies between 1-10 MHz, compared to the LO generator based on an X-tal oscillator and multiplier chain. The key component in this programme is the developed VCO MMICs.
One important issue is also to build up expertise in the MMIC VCO design at RUAG Space AB by the design work in close cooperation with Chalmers University.
To have a wide product portfolio based on different LO generation topologies, and to have a deep knowledge in how they can be used to meet demanding, future requirements on signal sources.
One part of the programme is the development of different VCO MMIC designs and the other part is development of a PLL EM unit, including the PLL hybrid. The VCO development includes investigation of novel MMIC technologies to meet the demanding, future requirements of LO generation within 1-20 GHz. Technologies of interest and used in the technology trade off are GaN, InGaP and SiGe. The following is important for the performance of the VCO device.
The main challenge in this program is to extend the tuning range so that it can be covered with as few VCOs as possible. To mitigate the risk, several different VCOs are developed.
a) One narrow-band oscillator targeting minimum phase noise
b) Three medium bandwidth oscillators together covering the full PLL band
c) A wideband oscillator covering as much as possible of the PLL band
The baseline LO frequency generator block diagram is shown in the figure below. The VCO frequency range for the PLL EM Unit is approximately 10 to 11 GHz.
The LO frequency shall be settable, within a given frequency range, by command (during manufacturing).
The Project was planned within two consecutive Tasks. Task 1 included all the system definition work, different LO solutions were investigated and the requirement specifications updated (VCO and PLL EM unit). Also technology trade off for the VCO topologies, VCO semiconductor process and foundry were performed in task 1. The task ended with a technology trade off review in October 2014. Task 2 included detailed design, manufacturing, integration and test for the VCO MMIC and PLL EM Unit, and ended in January 2017.
The measured main parameters including
were within specified limits as set up for the PLL EM Unit. Measured Phase Noise is as expected and in line with calculations. The VCO tuning range was sucessfully extended (up to +60 V) by design of a new loop filter.
However the current status for the GaN technology is that it suffers from high 1/f noise which significantly degrades the phase noise performance.
The most significant achievements of the project also involve higher understanding of VCO design and modelling in general, and special in design and manufacturing a MMIC VCO using GaN technology.
A GaN varactor model based on measurements and suitable for phase noise simulations was also developed within the project and possible through the close cooperation with Chalmers University.
All activities are completed: