With the increasing number of mobile communication standards, a large research effort is put into the task of complete integration of RF voltage-controlled oscillators (VCOs) for multi-band and multi-mode direct conversion transceivers. However, RF VCOs are, at present, not fully integrated in transceivers, since they suffer from poor phase noise and fabrication tolerances.
The cross-correlation method allows phase-noise measurements of high-quality devices with very low noise levels, using reference sources with higher noise levels than the device under test. To implement this method, a phase-noise analyzer needs to compute the cross-spectral density, that is, the Fourier transform of the cross-correlation, of two time series over a wide frequency range, from fractions of Hz to tens of MHz. Furthermore, the analyzer requires a high dynamic range to accommodate the phase noise of high-quality oscillators that may fall off by more than 100 dB from close-in noise to the noise floor at large frequency offsets. This paper describes the efficient implementation of a cross-spectrum analyzer in a low-cost FPGA, as part of a modern phase-noise analyzer with very fast measurement time.
Design and verification of a low-noise amplifier with electrical isolation between the sensor and load.
ObjectiveThe objective of this experiment is to design, simulate, evaluate, and document a low-noise amplifier circuit.
SpecificationsA basic circuit diagram of the amplifier is shown in Fig. 1. The low-noise amplifier is to have one input and one output. The amplifier is to employ a unipolar + 9 V or +15 V dc power supply. A 4N25 electro-optical isolator is to be used to isolate the source from the load. The source resistance of the sensor is to be R s = 6.8 kΩ. A preamplifier is to be used between the sensor and the isolator and a post amplifier between the isolator and load. The active devices used in these two amplifier will be discrete transistors. The load resistor is to be R L = 12 kΩ.The maximum value of the amplitude of the open circuit voltage produced by the sensor is to be 10 mV.The sensor drives a preamplifier which is ac coupled to the electro-optical isolator. The output of the isolator is amplified by the post amp to supply the output signal to the load resistor. The post amp should contain a coupling capacitor to keep dc off the load.
Design Goals• The maximum output SN R ≥ 50 dB (V so /V no ) with an input signal of 10 mV peak sine wave at a frequency of 3.2 kHz.
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