With a suitable choice of bias, it is possible to have a stable amplifier when the input is connected to a resonant circuit, obviating the need for an isolator.Ī two-port microwave network is conveniently described by a scattering matrix relating the voltage V + incident on one port with that ( V − ) scattered from the same or a second port.
#If stability circle outside smith chart full#
In this letter, we report measurements of the full set of complex scattering (S) parameters of the MSA, and use them to demonstrate that the MSA is conditionally stable. Unless the amplifier is unconditionally stable, however, this may lead to unstable behavior and loss of amplification. A desirable alternative is to connect the amplifier directly to the measurement circuit. Isolators require a magnetic field to break time-reversal symmetry, and are often noisy, lossy and bulky. To tame the effects of a complex source impedance one typically inserts an isolator between the source and the input. In both cases, the source impedance is a complex function of frequency. In a typical application, such as axion detection 1 or dispersive qubit readout, 11 the MSA is used to measure the frequency response of a resonant cavity or circuit. With appropriate current and flux biases, the SQUD converts an input flux Φ to a voltage V with a transfer function V Φ ≡ ∂ V / ∂ Φ. At the fundamental resonance, there is substantial coupling between the magnetic field of the microstrip mode and the SQUID. A thin dielectric layer covers the washer, and a square coil deposited over it to form a microstrip resonator. 1 The MSA consists of a superconducting square washer 10 interrupted by two resistively shunted Josephson junctions. The microstrip SQUID (Superconducting quantum interference device) amplifier (MSA), 4 cooled to millikelvin temperatures, offers both a gain in excess of 25 dB and a noise temperature within a factor of two 8 of the standard quantum limit 9-typically 50 times lower than that of a high electron mobility transistor. In the section Smith Chart Available Gain Circles you can specify number of circles and increment value.A growing number of applications including a search for dark-matter axions, 1 the readout of superconducting qubits 2 and a postamplifier for the radio-frequency single electron transistor 3 require high-gain, low-noise amplifiers 4–7 at frequencies around 1 GHz. To configure number of circles drawn and the increment, go to Options dialog box ( Tools->Options… menu) and select NPAR File Propertiesicon. The Available Gain Circles will be drawn in the Smith Chart (green circle) in the Separate 4 Noise Parameters (npar files only) tab and NFmin-AvGain and Rn tab. s2p file containing the available gain circles data opened in the viewer in a separate file tab. To add Available Gain Circles to the first Smith Chart (top-left), the user needs to have. The circles will be red except for the circle corresponding to the current frequency circle which will be yellow. The Smith chart on the left hand side will draw all the circles for all frequencies. To modify current frequency use the scroll bar at the bottom of the view. The Smith chart on the right hand side will draw only one circle corresponding to the current frequency. The stability circles will be drawn in the two Smith charts in the Separate 4 Noise Parameters (npar files only) tab. s2p file containing the stability circles data. s2p file, right click on the file tab and select Add To View Stability Circle (.s2p)… from the context menu. s2p file containing the stability circles data opened in the viewer in a separate file tab. To add Stability Circles to the first Smith Chart (top-left), the user needs to have. The Stability Circle represents the area of the Smith Chart in which the devise can become unstable. Category: FDCS Noise Measurements / Data Explorer
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