TZA400

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 t ...Read more

The transimpedance amplifier TZA400 is
designed for precise measurement of current,
from pA to mA. The output is a voltage linearly
proportional to the input current. 

The gain of the TZA400 may be controlled via
USB or the hard-wire interface control. A
graphical user interface is delivered with the
amplifier.
 

CHARACTERISTICS

Interfaces: USB and hard-wire (DB25)
Rise time: 1µs (G≤5x105); 4µs (higher gains)
Noise equivalent current: 500 p(ARMS) 
Gain control: 16 gain ranges in 1-2-5 pattern or
4 gain ranges in decade spacing



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.

 

- Number of gains: 4, 16

- Case: gull wing, lab style, 19” rack module

- Number of channels: 1, 2, 3, 4

 

Manual gain switch dongle for hardwire interface.

 

What does an output impedance of 50Ω mean?

The output impedance of an amplifier is an important factor when dealing with fast signals. The speed of the TZA400 is fast enough for this parameter to be relevant. Essentially, the output of the amplifier is a 50Ω resistance in series with the output. This allows you to terminate the signal line with a 50Ω resistance to prevent back reflections. The result is a clean signal transient without overshoot. The disadvantage is that the signal voltage is halved by doing this. The amplifier may be used without the 50Ω termination resistance, but then there will be overshoot when amplifying fast transients.

 

What does an output impedance of 50Ω mean?

The output impedance of an amplifier is an important factor when dealing with fast signals. The speed of the TZA400 is fast enough for this parameter to be relevant. Essentially, the output of the amplifier is a 50Ω resistance in series with the output. This allows you to terminate the signal line with a 50Ω resistance to prevent back reflections. The result is a clean signal transient without overshoot. The disadvantage is that the signal voltage is halved by doing this. The amplifier may be used without the 50Ω termination resistance, but then there will be overshoot when amplifying fast transients.


What is a BR2 connector?

The outer dimensions and style of connection action of the BR2 connector are identical to BNC. However, instead of one centre pin, the BR2 has two inner pins beside each other (with the shielding braid around both of them). The use of BR2 connectors and shielded, twisted pair cable reduces noise considerably when measuring remote current sources in a noisy environment.


How can I measure a grounded source?

In order to measure a grounded source, the amplifier must have a single ended input configuration. You may use either the BNC or BR2 receptacle.


What is a differential input?

Often we think of a current source as having only one connection, however the other connection is just as important: it is the current return path. A differential input has an active amplifier input for both connection points to the current source. The outputs of these two amplifiers are then electrically subtracted. This has the effect of doubling the signal voltage (since the return path current is of opposite polarity), but cancels any noise components which were equal on both electrodes (“common mode” noise).

 

Spezifikationen TZA400