Technical Info Key Consideration When Selecting a Preamplifier The most important role of a preampliﬁer is to faithfully amplify the input signal. The ideal preampliﬁer should be providing a suﬃcient wide range, generating no noise by itself, no waveform distortion, hardly being aﬀected by temp. change and over time change. It’ s important to select the optimal preampliﬁer for the application under speciﬁc conditions. 1 Input Signal Level In some applications, gain may be set using several stages of ampliﬁers due to a very low input signal level. In such setups, it’ s particularly important to use a low-noise ampliﬁer in the initial stage since any noise generated there will be ampliﬁed by the following stage. 2 Gain There are ﬁxed gain ampliﬁers and switchable gain ampliﬁers. If the input signal level is unknown or greatly changed, selects a switchable gain ampliﬁer. 3 Input Mode There are a single wire ground input and a diﬀerential input. If the gain and the frequency characteristics are same, the ampliﬁer with single wire ground input achieves lower noise. If the external noise is large, you can reduce the inﬂuence of external noise by using a diﬀerential input ampliﬁer. " 4 Signal Frequency Range We should consider whether we need the ampliﬁer to accommodate DC at the lower end of the frequency range and what the upper limit of that range will be. Ampliﬁers with a wide range exhibit fast response and produce waveforms with a faithful leading edge. However, a wide range also results in more noise, so we should choose an ampliﬁer that matches the frequency of the signal. / Key Consideration When Selecting a Preamplifier Technical Info 5 Input and Output Impedance The ideal low-frequency ampliﬁer has suﬃciently high input impedance and low output impedance. As for high-frequency ampliﬁer (over 10 MHz), its input and output impedance should match with a coaxial line" (50 Ω in general) 6 For Current Output Sensor Uses If you use the current-output sensor, select a transimpedance ampliﬁer (Current to voltage converter) . In this case, the ampliﬁer should have low input impedance. Since the capacitance of the sensor aﬀects the ampliﬁer’s frequency characteristics, the input cable length between the sensor and the ampliﬁer should be minimized. It’ s also necessary to consider factors such as the ampliﬁer’ s maximum output voltage, input noise, input oﬀset, oﬀset drift, distortion, size, power supply, and power consumption. Products Low Noise Preamplifier SA-230F5 (voltage amplifier) Frequency range: 1 kHz to 100 MHz Input type: Single-ended Input impedance: 50 Ω Equivalent input noise voltage density: 0.25 nV/√ Hz Noise ﬁgure: 0.6 dB Gain: 46 dB Wideband Current Amplifier SA-604F2 (current to voltage converter) Frequency range: DC to 500 kHz Input type: Single-ended Input impedance: 1 kΩ Equivalent input noise current density: 45 fA/√ Hz Gain (V/A): 1×107 (10 M) Low Noise DC Power Supply LP5393 Output Noise: 10 µVrms or lower (typ.) (10 Hz to 20 MHz bandwidth) Output Voltage Stability: ±20 ppm/°C (typ.) Output Voltage: ±12 V to ±15 V Output Current: ±0.1 A max.
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