Johnson noise


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Related to Johnson noise: white noise, current noise

Johnson noise

[′jän·sən ‚nȯiz]
(electronics)
References in periodicals archive ?
* very low voltage noise referred to the input of the amplifier: At the TPW temperature, the Johnson noise voltage across the sense resistor is only 0.123 nV [[ohms].sup.-1/2] [Hz.sup.-1/2], resulting in a noise voltage of 1.74 nV [Hz.sup.-1/2] for a 200 [ohms] sense resistor, as used in these measurements;
* wide bandwidth, high amplification, and flat transfer characteristics in the passband of the amplifiers; for a transmission bandwidth of 1 MHz, the root-mean-square Johnson noise voltage would increase to 1.74 [micro]V; and
We then apply this approach to measure the temperature of a sense resistor that is collocated with the JJ arrays on the QVNS chip and use the symmetry of the measurement channels to directly determine the undesired correlated noise in our JNT system, which is not related to Johnson noise.
To restate the JNT data analysis procedure, we start by defining complex, frequency-dependent voltage transfer functions [H.sub.A,R] (f) and [H.sub.B,R] (f) between the Johnson noise voltage source [V.sub.R] and the input to the amplifier on channel A and channel B, respectively (see Fig.
(2), we have also added the possibility of undesired correlated noise, [C.sub.n,R] = [V.sub.A,n,R][V.sup.*.sub.B,n,R] due to some voltage noise source at the input to the amplifiers that is not related to, or correlated with, the Johnson noise. [C.sub.n,R] can be both complex and frequency-dependent.
For the Johnson noise source, we sum the measured cross-correlation across a bandwidth [DELTA]f surrounding the frequency combs.
To directly measure the presence of correlated noise, we modified the NIST JNT system to measure Johnson noise at 4 K from resistors collocated with the QVNS source (see Fig.
(4), requires subtraction of the measured Johnson noise [C.sub.R] from the measured cross-correlator at the QVNS tone frequencies [C.sub.Q] before taking the ratio
Finally, we describe our measurements of the triple point of water temperature realization and the resistance of the Johnson noise sense resistor.
In practice, the inherent differences in the output impedance of the JJ arrays in the QVNS (which are purely inductive) and the Johnson noise source (which is purely resistive and 200 [ohms] in this experiment) and the required physical locations at cryogenic temperatures and in a TPW cell, respectively, make matching the transfer functions difficult.
[37], is to fabricate resistors on the QVNS chip to partly match the output impedance of the 200 [ohms] Johnson noise resistor.
The resistance of the on-chip QVNS resistors is slightly smaller than the Johnson noise resistor.

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