PRINCIPLES OF OPERATION
The TZA400 measures small currents e.g. optical power via a photodiode. Photodiodes are useful for power measurement in the visible and near infra-red due to their inherent sensitivity and speed of measurement.
Photodiodes produce a current which is proportional to the incident light power over a wide dynamic range.
The current is converted to a voltage through a precise transimpedance amplifier. This amplifier is very linear over the full measurement range of the device. The TZA400 has optionally 4 or 16 gain ranges. The switch is a semiconductor device, free from degradation.
The analogue output signal is available at the BNC connector on the front panel an on the appropriate line on the interface port on the back panel.
The voltage generated is then converted to a digital value via a 12 bit A/D converter. This process and all calculations and communication with the PC are controlled by a microcontroller. The measurement process is started via a command over the USB interface (software trigger). Alternatively, a continuous measurement stream can be started which samples at 1.5 kS/s. The measured photocurrent may then be read out from the USB port.
FIELDS OF APPLICATION
These transimpedance amplifiers are particularly useful for the measurement of current from photodiodes. The output is a voltage linearly proportional to input current and thus, to input power in photodiode monitoring applications. The fast response time at high signal-noise ratio makes the TZA400 series particularly useful in systems control feedback loops.
These amplifiers have a particularly high sensitivity and large dynamic range. There are 16 gain ranges covering 5 decades of gain in a 1-2-5 pattern. The gain-to-gain accuracy of <1% allows confident measurements of power curves over the full range of sensitivity of the device: 6½ decades of measurement range. Thus even very demanding measurements such as the accurate and high speed, real-time determination of polarization extinction ratio becomes a simple task.
The TZA400 series is insensitive to electromagnetic interference by design, an important factor when working in „dirty“ industrial environments. These units are provided in a modular 19“ rack mount system.