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  • ADA4530 Electrometer-Grade Amplifier

  • Created: Feb 22, 2016

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This design is used to evaluate the ADA4530 femtoampere (10^-15 A) level input bias current operational amplifier, suitable to be use as an electrometer. It has an operating voltage range of 4.5V to 16V enabling it to operate in conventional 5V and 10V single supply systems as well as ±2.5V and ±5V dual supply systems. The board also offers low offset voltage, low offset drift, and low voltage and current noise needed for the types of applications that require such low leakages. To maximize the dynamic range of the system, it has a rail-to-rail output stage that can typically drive to within 30mV of the supply rails under a 10kΩ load.

The board is available in two default configurations: buffer (EBZ-BUF) and transimpedance (EBZ-TIA). Both boards are populated with the necessary passive components, banana jacks/terminal blocks for supply voltages, and BNC/terminal blocks for the output voltage, multiple test pins, and metal shields. All components are placed on the primary side with the exception of the triaxial (triax)/ coaxial (coax) input connector (J1) and SHIELD3. The board also has unpopulated resistor and capacitor pads that allow quick prototyping with different configurations, such as noninverting gain and inverting gain.

The amplifier on this evaluation board is defaulted to a buffer configuration. An input signal can be applied through the triax connector, J1. Note that JP3 is left unconnected by default so that the triax guard can be driven by external test equipment. For this configuration where the triax guard is not driven by any external test equipment, TRIAX GUARD must be shorted to AMP GUARD via JP3. This configuration is useful when the buffer is connected to a passive sensor. The transimpedance configuration is a current-to-voltage (I to V) converter. A 10GΩ feedback resistor (RF1) is preassembled on board. If other resistor values or package sizes are needed, the 10GΩ feedback resistor can be desoldered to allow the assembly for the SMT resistor of choice. It can also be reconfigured to allow direct sensor connection. To reconfigure the board, remove the input BNC connector (J1). The user must then access Pin P6 (the inner conductor pin of the BNC connector). Assemble the photodiode of choice between P6 and the signal ground.

The ADA4530 can be used on applications like laboratory and analytical instrumentation (spectrophotometers, chromatographs, mass spectrometers, and potentiostatic and amperostatic coulometry), instrumentation (picoammeters and coulombmeters), high impedance buffering for chemical sensors and capacitive sensors, and transimpedance amplifier for photodiodes, ion chambers, and working electrode measurements.



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