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Model 5402 Low Noise Current Amplifier

Model 5402The Model 5402 is a low noise current input preamplifier designed for use whenever the signal source is a current source – for example, an electron multiplier, ion collector, photo multiplier, or photodiode, or when measuring sample impedances. The gain (transimpedance) is switch selectable with six settings enabling the amplifier, on its most sensitive range, to detect fractions of a picoamp without noise degradation.

The unit has a bandwidth of 100 kHz on its highest gain (1 GV/A) and greater than 4 MHz on its lowest gain (10 kV/A), while still maintaining low input current noise ranging from 25 fA /√Hz on the 1 GV/A range to 5 pA/√Hz on the 10 kV/A range. The gain setting is changed by simply pressing a push-button, with the present setting being indicated by an LED. The setting is retained when the power switch is turned off and restored when it is turned on again.

Switch selectable output filters allow AC or DC output coupling, and three choices of low pass filtering which can reduce overall noise, especially when working at high gains if the full bandwidth is not required.

The Model 5402 is powered by two internal lithium-ion rechargeable batteries which allow operation for up to 48 hours on a single charge. This method of powering delivers the lowest possible noise as well as allowing isolated operation, preventing problems which might be caused by ground loops.

A plug-in line power supply, model PS0112, is included which is capable of recharging the batteries in one model 5402; recharge time is a maximum of three hours.

Model 5402 specs

 Mode Single-ended
 Coupling DC
 Connector BNC socket
 Maximum safe input voltage ±20 V DC
 Input Bias Current 1 pA typical
 Input Referred Voltage Noise 2.5nV/√Hz typical
 Input Referred Current Noise See Table Below
Gain & Frequency Response
 Gain Switch selectable (6 settings) to 1G, 100 M, 10 M, 1 M, 100 K, 10 K V/A
 Accuracy ± 0.5 dB
 Flatness in pass-band ± 0.5 dB
 Frequency Response See Table Below
 Cut off frequency settings:
     10 M Full bandwidth
     1 M 1 MHz ± 150 kHz
     110 k 100 kHz ± 15 kHz
Output Filters
 Output Coupling (high-pass) When set to DC, amplifier is DC coupled.
When set to AC, low- frequency cut off is 0.1 Hz
 Output Filter (low-pass) Low pass Butterworth filter with 18 dB/octave roll-off filter reduces overall noise, especially when working at high gains, if full bandwidth
is not required.
 Impedance 50 Ω
 Connector BNC jack
 Max voltage swing > 5 V pk-pk
 Polarity Current flowing into the input produces a positive output voltage
 Protection Output is short-circuit protected
 Internal Rechargeable lithium ion batteries provide up to 48 hours of use.
Batteries recharge automatically when DC power is connected. Recharge time is max of 3 hours
 External 9 V DC @ 350 mA max
 Connector 1.3 mm DC power socket, inner pin positive, outer barrel negative
 Excluding connectors  3½” w x 1¼” d x 2¾” high
(85 mm x 31 mm x 71 mm)
 Including connectors  4½” w x 1¼” d x 2¾” high
(114 mm x 31 mm x 71 mm)
 Weight 7.5 oz. (210 g) excluding optional power supply

Typical Frequency Response Table

Gain  Bandwidth (–3dB) with
Cin = 10 pF 
 Bandwidth (–3dB) with
Cin = 1 nF 
 Input Referred
Current Noise (typical
 10 K > 4 MHz > 600 kHz 5 pA/√Hz
 100 K > 2 MHz> 400 kHz 880 fA/√Hz
 1 M > 1 MHz > 200 kHz 300 fA/√Hz
 10 M > 800 kHz > 100 kHz 140 fA/√Hz
 100 M > 250 kHz > 50 kHz 65 fA/√Hz
 1 G > 100 kHz > 25 kHz 25 fA/√Hz
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