Driving the future of technology : Original solution in measurement and control

 Lecture for Measurement

Posted 2019/7/19

Voltage amplifier ("voltage to voltage amplifier")

NF voltage amplifier

3. Points concerning use of the SA series

In combination with a low-noise power supply

When constructing a measurement environment with low noise, the power-supply environment is the most bothersome task to the last. Moreover, in the case of the 50-Hz-to-several-kHz band (covering a commercial power supply and its harmonics), it is difficult to remove the frequency band to be measured with a filter, and various countermeasures are often being repeated in different ways.

Traditionally, the final countermeasure against the noise was power by battery. However, no matter how large the capacity of the battery used, it is necessary to replace the battery or re-charge it. The voltage supplied from the battery gradually decreases during use. And as temperature changes, voltage fluctuates. From the viewpoint of long-term operation, it can be said to be a lack of stability in the power supply. Therefore, achieving low noise by utilizing battery power is only a solution regarding short-time operation.

Accordingly, to solve these power-related problems, we have prepared a low-noise power supply specialized for low-noise applications.

Model Product name Description
LP5394 Low-noise DC power supply LP5394 is recommended for driving SA series.
For applications in addition to the drive power supply, such as a reference-bias source from 0 V to ±15 V.

As for the extent of how much noise can be lowered, it is said that “noise measurement is impossible unless the object is amplified with an extremely low-noise amplifier.” Even if it is attempted to observe the noise waveform as is with an oscilloscope, so-called ripple voltage does not appear at all. Because noise is that low, for example, the signal can be directly used for one input of the differential amplifier circuit (as a reference-voltage source) and the reference-bias source of the sensor.

About output termination of the SA series

Among the SA series, the units with AC-coupled inputs (SA-220F5, SA-420F5, etc.) are designed to have a gain of 46 dB (200 times) when their output is terminated at 50 Ω. Regarding performance other than gain, it is specified when terminating at 50 Ω.

Ensure to set the input impedance to 50 Ω when connecting the output of SA series units with input AC coupled to equipment such as an oscilloscope.

For equipment that cannot be set to 50 Ω, use a commercially available 50 Ω terminator. If a device with high input impedance (such as 1 MΩ) is connected as is, the specified performance (e.g., frequency characteristics) cannot be obtained.

Related Product

Extremely low noise amplifier SA Series

Extremely low noise, excellent stability, wideband preamplifier for detection of extremely small signals

     Low noise
  • Adopted our exclusive circuit applying negative feedback technology
    SA-230F5: at input impedance of 50 Ω, noise figure of 0.6 dB and equivalent input noise voltage density of 0.25 nV/√Hz
  •  Wideband
  • A wide frequency band from low-frequency signals including DC (SA-200F3/240F5/410F3/440F5) to high-frequency, high-speed signals (SA-250F6/251F6) exceeding 100 MHz is covered.
  •  Input mode according to signal source
  • Single-ended (single-wire-grounded) input, single-ended FET input, differential input, and differential FET input



Related keywords :  Ultra low noise amplifier, LNA

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