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Current to Voltage Preamplifier, Low Noise
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Converts Current to Voltage - Ideal for PMTs and photodiodes

This preamplifier converts the current from an unamplified detector, a photomultiplier tube, solar cell or other sensor to a voltage output. This allows the output signal to be read by a lock-in digital amplifier, which is able to separate small signals from background noise. Although Newport's LIDA-SRS-KIT-120V and LIDA-SRS-KIT-220V models read both current and voltage, voltage signals are generally preferred. The wider dynamic range of the instrument, when reading voltage signals, means that the same signal when read as current may saturate the detection instrument. If an amplified signal from the 70710 will be read by one of Newport's DC power meters, use the 71686 adapter to connect the BNC signal cable from the preamplifier to the meter. If read with either LIDA-SRS-KIT, use BNC signal cable 70018 to connect the preamplifier to the lock-in.

Six Amplifier Selections

One of the most practical features of the 70710 is that it has six switchable amplifier selections, 104, 105, 106, 107, 108 and 109 volts per ampere. The 70710 also has a three position time constant switch. Standard BNC input and output connectors facilitate connection to other devices. Amplifiers always require power to operate. The 70710 must be powered by an external ±15 V supply such as our model 70703 or 70709 lab power supply. We provide a power cable with banana jack terminals for connection to our lab power supply or other ±15 V source.

Low Noise and Wide Dynamic Range

The 70710 has wide dynamic range and linearity. The volts per ampere conversion ratio is determined by the switch setting. Changing the switch changes the feedback resistor. The input impedance, i.e. the apparent resistance, which the amplifier displays at its input, equals the feedback resistance divided by the gain of the operational amplifier (which is at least 150,000) plus a 1,200 ohm isolation resistor at the amplifier’s input. A feedback resistor of 106 ohm corresponds to a conversion ratio of 106, etc. The input impedance is then 106/150,000 or about 7 ohms plus the 1,200 ohm isolation resistor. Even at the 109 V/A setting, the input impedance is only about 8,000 ohms. These relatively low impedances are essential for obtaining a wide linear dynamic range from photodiodes.

Wide Bandwidth - DC to 100 kHz

The preamplifier bandwidth depends on the gain setting and the selected time constant.