Overview
The model 181 is a current-to-voltage preamplifier of low noise and low input impedance designed to amplify the extremely low currents encountered in such areas as photometry and semiconductor research. In photometric applications the low input noise allows the use of photodetectors with dark currents as low as 10-14 A/√Hz, while the wide frequency range permits high modulation frequencies to avoid 1/f noise and power-line pick-up.
The unit has a high dynamic range, allowing small AC currents to be amplified without overload in the presence of quiescent (DC) detector currents up to ten times the current to voltage converter setting. In semiconductor applications its low input impedance permits the actual bias voltage applied to the device under test to be measured without having to correct for the effects of back bias.
Six switch-selectable sensitivity settings from 10-4 A/V to 10-9 A/V are available and the instrument has a usable frequency range from DC to 200 kHz. A signal monitor connector is provided on the rear panel and there is an overload indicator light on the front panel.
Bias Control
A bias control (accessible through an opening in the bottom of the unit) allows the application of a detector bias voltage at the input connector in the range 0 V to -5 V, with a nominal source impedance of 10-5/S, where S is the selected sensitivity. For example, if the sensitivity is set to 10-7 A/V then the source impedance will be 10-5/10-7, or 100 Ω. In some cases it
may prove convenient to use this bias control to cancel the effect of DC bias accompanying the input signal.
DC Zero Control
A second control, also accessible through an opening in the bottom of the unit, allows the internal electronics to be DC zeroed.
Power
The unit can be powered from an external low voltage, a lock-in amplifier via a suitable power cable, or the models PS0055 or PS0056 remote line power supply modules.
- Low input impedance
- Low noise
- Single-ended virtual ground input
- Adjustable sensitivity
- DC to 200 kHz frequency response
- Detector bias control
- Photodiode amplification
- Photomultiplier amplification
- Ion collector amplification
- Electron multiplier amplification
Specifications
General
DC coupled current to voltage amplifier with adjustable sensitivity and a maximum frequency response extending from DC to 200 kHz. Adjustable negative detectors bias. Single-ended virtual ground input and single-ended AC coupled output via BNC connectors.
Powered from external DC power supplies.
DC coupled current to voltage amplifier with adjustable sensitivity and a maximum frequency response extending from DC to 200 kHz. Adjustable negative detectors bias. Single-ended virtual ground input and single-ended AC coupled output via BNC connectors.Powered from external DC power supplies.
| Input | |
| Sensitivity | 10-4 A/V to 109 A/V in six angles |
| Overload Indicator | Indicates that instantaneous (DC plus peak AC) current has exceeded amplifier capability – see table below |
| Frequency Response | see table and Figure 1 |
| Input Impedance | See Figure 2 |
| Noise Current | See Figure 3 |
| Outputs | |
| Monitor Output | 600Ω rear-panel BNC connector permits monitoring of the input signal |
| Main Output Level |
6.5 V rms maximum |
| Impedance | 1Ω k nominal |
| Output Attenuator | Provides optional 1:10 attenuation of output voltage |
| Power | ±15 V or ±24 V at 30 mA |
| General | |
| Dimensions (excluding connectors) | 4.5" wide x 6.6" deep x 2.7" high (114 mm wide x 168 mm deep x 69 mm high) |
| Weight | 1.2lbs. (500 g) |
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