RF probe

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An RF probe is a device which allows electronic test equipment to measure radio frequency (RF) signal in an electronic circuit.

Contents

History

In 1980 Reed Gleason and Eric Strid invented the first high frequency wafer probe while working at Tektronix. They later went on to found Cascade Microtech in 1983. [1]

RF energy may be challenging to measure for one or more reasons, depending on the nature of the circuit to be measured and the measuring equipment at hand.

The first kind of difficulty arises when the RF energy to be measured is at a frequency too high for available test equipment, such as a low-bandwidth oscilloscope, to process directly. In that case, the RF has to be converted to a DC or near-DC signal.

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In this situation, a simple probe type sometimes called an RF detector can be used to convert the RF signal to DC. Such device will work as a RF rectifier and give a pulsed DC voltage. [2]

The second kind of difficulty arises when RF energy has to be measured in a circuit which is sensitive to small changes in its electrical environment. For example, with some oscillator circuits, the presence of an ordinary wire within a few centimeters of the active components may change the amplitude or frequency of oscillations, or even prevent the circuit from oscillating at all. In that case, the signal has to be acquired by a measurement probe which extracts very little energy from the circuit. This can be achieved by employing very thin conductors, or tiny coils kept at some minimum separation from the active elements of the circuit.

In a situation, where circuit loading rather than high frequency is the real problem, a variety of small-geometry, high impedance probes can be used, sometimes including an amplifier to boost the tiny amount of energy extracted from the circuit to a level that allows it to be measured by available high-frequency test equipment.

Coaxial structures with spring-loaded inner and outer conductors can serve as an RF probe for modern communication electronics. Such probes are for instance being used in mass-production, in-line testing of communication electronics such as mobile phone industry. [3] RF probes are especially relevant for switches and RF traces in printed circuit boards as well as terminations of RF components. In such systems, like many other RF circuits, there is a higher requirement of matching probe impedance with that of the DUT. Efficient matching avoids reflection which in turn leads to efficient power transfer. The second challenge to keep the power transfer efficient, is to keep the insertion loss as low as possible. Optimizing these parameters generally gets more challenging as the frequency increases.

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A Q meter is a piece of equipment used in the testing of radio frequency circuits. It has been largely replaced in professional laboratories by other types of impedance measuring devices, though it is still in use among radio amateurs. It was developed at Boonton Radio Corporation in Boonton, New Jersey in 1934 by William D. Loughlin.

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A network analyzer is an instrument that measures the network parameters of electrical networks. Today, network analyzers commonly measure s–parameters because reflection and transmission of electrical networks are easy to measure at high frequencies, but there are other network parameter sets such as y-parameters, z-parameters, and h-parameters. Network analyzers are often used to characterize two-port networks such as amplifiers and filters, but they can be used on networks with an arbitrary number of ports.

Charge amplifier

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An oscilloscope, previously called an oscillograph, and informally known as a scope or o-scope, CRO, or DSO, is a type of electronic test instrument that graphically displays varying signal voltages, usually as a calibrated two-dimensional plot of one or more signals as a function of time. The displayed waveform can then be analyzed for properties such as amplitude, frequency, rise time, time interval, distortion, and others. Originally, calculation of these values required manually measuring the waveform against the scales built into the screen of the instrument. Modern digital instruments may calculate and display these properties directly.

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An LCR meter is a type of electronic test equipment used to measure the inductance (L), capacitance (C), and resistance (R) of an electronic component. In the simpler versions of this instrument the impedance was measured internally and converted for display to the corresponding capacitance or inductance value. Readings should be reasonably accurate if the capacitor or inductor device under test does not have a significant resistive component of impedance. More advanced designs measure true inductance or capacitance, as well as the equivalent series resistance of capacitors and the Q factor of inductive components.

Nominal impedance in electrical engineering and audio engineering refers to the approximate designed impedance of an electrical circuit or device. The term is applied in a number of different fields, most often being encountered in respect of:

References

  1. ↑ "RF & Microwave Probes for Test & Measurement - everything RF".
  2. ↑ http://www.instructables.com/id/RF-probe/Instructables, RF Probe
  3. ↑ Zapakta, M.; Ziser, R. (2008). "An introduction to coaxial RF probing solutions for mass-production tests".Cite journal requires |journal= (help)
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