오실로스코프 프리 앰프

 The LNA 10 oscilloscope preamp will significantly improve the small-signal performance of oscilloscopes at frequencies below 1MHz.   

Product Description:

With this preamp, sub-microvolt signals can be displayed on scopes which typically only go down to 1mV/div on the vertical axis.  The preamp includes an analog true differential input and an analog low-pass filter (tunable 1Hz-1MHz).  Input-referenced RMS noise spectrum for f >100Hz is 4 nV/√Hz or less, so for example, even with 1000 x gain, total noise from 100 Hz to 1000 Hz is less than 1 div peak-to-peak on a 1mV/div vertical scope setting (assuming a low-impedance input).  Most oscilloscopes are designed to display high-frequency (fast) events that may intrinsically have noise of a millivolt or more.  However, low-frequency signals have much less intrinsic noise, so a low-noise preamp and a bandwidth-limiting filter are essential for small signals at low frequency.* Most amplifiers have a white noise spectrum (a flat spectral curve) at all frequencies above ~1000 Hz.  This white noise spectrum is usually specified as a certain number of nV per √Hz.  However, unlike typical passive resistors, the equivalent input noise spectrum of solid-state amplifiers (in nV/√Hz) becomes higher at low frequencies.  Typically the number of nV/√Hz is proportional to ~1/f for f ≤10Hz. The table below shows actual noise of the LNA 10 in various frequency ranges. At all frequencies, the LNA 10 has much less noise than typical solid-state amplifiers.

*The intrinsic “white” noise of a resistive electrical circuit at room temperature is proportional to √(R∙Δf), which is the square root of the product of source resistance multiplied by the bandwidth being investigated.  For low source resistance and low frequencies, noise is low.  For example, a 1000 Ω resistor will have an intrinsic RMS noise of 13 nV in a Δf =10 Hz bandwidth, with 10 Hz being the bandwidth, for example, associated with the frequency range 0-10 Hz,  or with the frequency range 102 Hz-112 Hz.  The noise will become twice as much if the bandwidth being studied is 4 times as wide (i.e., 40 Hz), or if the resistance is multiplied by 4.

1 microvolt peak-to-peak square wave, 3 Hz (amplified 1000 X)

 Features

• Output has a single pole lowpass filter, tunable from 1 Hz to 1 MHz. This feature reduces the bandwidth, as needed.
• Selectable DC/AC coupled input (“AC” passes through a .3Hz highpass filter, 1 pole): On DC, each input must be between -0.4V and +0.4V, with respect to case ground, for accurate readings. When set to AC, a DC offset up to +/- 30V can be present. (However, if the inputs rapidly vary by more than .8V peak-to-peak, then the slew rate must be ≤ 2V/sec for accurate amplification.)
• Inputs are protected to +/- 5KV static and +/-30V unlimited current transients, with respect to case ground.
• Selectable gains are 10x, 100x, 1000x (true differential, with CMRR > 90dB). Also positive and negative single-ended inputs can be selected, as well as reference ground. Gain accuracy: +/-1%. (The LNA 10 does not include a 1x gain.)
• An offset adjustment, equivalent to +/- 1 mV at the input, is present.
• A BNC output (100 Ω) is intended to be connected to a single oscilloscope channel, or to another voltage-reading device (data logger, voltmeter, etc).