Model 181
Current Sensitive Preamplifier
General
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/root 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 gain settings from 10-4 A/V to 10-9
A/V are available and the instrument has a useable 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 W.
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.
Frequency Response (typical)
Input Impedance (typical)
Noise Current (typical)
Peak Input Current (typical)
Gain
A/V |
Frequency response
DC to |
Maximum (peak) Input Current |
| 10-4 |
200 kHz |
1 mA |
| 10-5 |
200 kHz |
100 µA |
| 10-6 |
100 kHz |
10 µA |
| 10-7 |
50 kHz |
1 µA |
| 10-8 |
10 kHz |
100 nA |
| 10-9 |
1 kHz |
10 nA |
| Gain |
10-4 A/V to 10-9 A/V in six
ranges |
| Overload Indicator |
Indicates that instantaneous (DC plus peak AC) current
has exceeded amplifier capability - see table above |
| Monitor |
600 W rear-panel BNC
connector permits monitoring of the input signal |
| Output Attenuator |
Provides optional 1:10 attenuation of output voltage |
| Signal Output |
|
|
Level |
6.5 V rms maximum |
|
Impedance |
1 kW nominal |
| Power Requirements |
±15 V or ±24 V at 30 mA |
| Dimensions (excluding
connectors) |
4.5" wide x 6.6" long x
2.7" high
(114 mm wide x 168 mm long x 69 mm high) |
| Shipping Weight |
2.2lbs (1 kg) |
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is
a trademark of AMETEK, Inc.