The measurement control and evaluation software runs on this PC. From the point of view of the measurement control there is no special requirement towards the PC. The later evaluation of the measured data, however, requires a rather fast PC (200 MHz+).
Figure 2-2: The general diagram of the tester
The digital control unit of T3Ster controls both the power driver units and the measurement channels and organizes all the data flow between the PC and the equipment.
The equipment contains a controlled, programmable voltage source unit that switches between two programmed voltages. The switching time of the electronic switch is about 1ms. T3Ster also contains a controlled, programmable current source that switches between a programmed current value and zero. The switching time is about 1ms for switching off and slightly worse for switching on.
These two units can be used if the sensor/actuator on the thermal test chip is a BJT or a power MOSFET. In this case the current source provides a constant emitter (source) current. The current control is disabled in this case. The controlled voltage source provides the UCB (UDG) voltage. The dissipation step is IE*D UCB, resulting – in case of maximal allowed voltage and current values – a value of D Pmax @ 20W.
In case the device under test (DUT) is a diode-like device, the controlled current source provides the dissipation step. In this case we have to use a 3rd type built-in unit as well: the programmable sense current source. Both currents described above bias the diode in the powering phase. After switching-off the controlled source only the sense current remains on the diode and the equipment records the cooling transient. The maximum dissipation step is ~1V*2A @ 2W in this case.
The last power driver unit: the controlled switch is devoted to be used with conventional thermal test chips where a resistor serves as dissipator. In this case an external DC power supply has to be used and T3Ster is responsible only for the fast switching on/off of the current. (For voltages under 10V the controlled voltage source of T3Ster can also be used for this purpose – as shown in Figure 2-2). The ratings of the built-in electronic switch are 50V and 2A – thus dissipation-step values can be realized for up to 100W. Using the power booster unit (placed in a separate box) this range can be extended to 50V and 20A, that means up to 1000W (on special request a power driver unit with even higher ratings can be ordered). Using the controlled switch, the voltage is measured by the 4-wire method. Both the power current and voltage are measured using the A/D converters of T3Ster and are read by the computer.
All power driver units are provided with a 3-state panel-switch: OFF/PC/ON. The electronic switches are controlled by the PC only in case this panel-switch is in PC state. This way the previously programmed ON or OFF states can be steadily set for these sources, depending on the required measurement arrangement.
The safe operating area of the programmable voltage and current source refer to Figure 5-3 and Figure 5-4. For all suggested measurement arrangement the operating software supervises the programmed voltage/current values and prohibits the violation of these safety limits.
In case of conventional test chips the sensor is usually a diode or a resistor. The current of the operating point can be set by the programmable sense current source. The equipment is provided with four sense current sources that can be used independently. The same programmed value is set for all four sources.
The equipment has 8 slots for 8 identical measurement channels. The equipment can be ordered with the required number of measurement channels between 1 and 8. Each channel has its own A/D converter circuitry and data storage memory. This way, correct multi-channel measurements are possible, with a time resolution of 1ms. The voltage resolution is 12 bits and the noise amplitude is less than 2 bits. This means that the signal-to-noise ratio of the measurement is about 70dB. This high accuracy (typically 1 bit) is essential for the subsequent evaluation.
The measurement channels are provided with an internal, programmable compensation circuit. This circuit is needed by the diode thermometers where the ~0.7V forward voltage has to be compensated in order to measure only the voltage variation. The operating software carries out this compensation automatically. In order to use "MOS diodes" as sensors, the range of the compensation voltage extends to ± 5V.
The input voltage range is programmable: the ranges 50-100-200-400 mV are available. In the most sensitive range the temperature resolution (using a diode sensor) is about 0.01° C.
For thermocouple sensors an optional unit can be ordered: a preamplifier/cold junction unit, which is realized as a special cable with a measurement head. Using this option the resolution of the thermocouple measurements can be extended to 0.02° C.
The digital control (measurement arbiter) unit controls the measurement process. This unit involves a program memory loaded by the computer. The contents of the program memory determine both the sampling rate and the on-off switching of the power driver units.
The control words contain a POWER flag that sets the power drivers to their HIGH or ON state when switched on and sets them to their LOW or OFF state when switched off. The control words also contain the sampling rate for the measurement units stored in an exponential format. This means that the time interval between the actual and the next sampling can be individually determined (1ms, 2ms, 4ms, up to 8s) and the dissipation can be switched on/off individually for each sampling period. This construction offers an extreme versatility in the measurement sequences (exploited e.g. for sampling on a quasi-logarithmic time scale).
Figure 2-3 shows an example how the power driver units can be programmed (Set Measurement Parameters window) and how the measurement channels can be controlled (Set Measurement Channels window). The four Range buttons are for setting the input voltage range. The automatic compensation can be started from this panel, too.
Figure 2-4 presents a 1400 sec recording of the thermal transients of an MCM module, without cooling assemblies. Figure 2-5 is an enlarged part of the same function. These figures demonstrate clearly the excellent signal-to-noise properties of the tester and the very good resolution.
Figure 2-3: Screen-copy of the control software with panels of powering and
measurement channel settings
The measured "raw" transient curves can be evaluated from-within the T3Ster Measurement Control & Evaluation software (that is a mandatory part of any T3Ster configuration). As a result of evaluation, time-constant spectra, pulsed thermal impedance curves, complex loci of the measure impedance curves, and finally, so called structure functions can be extracted. These latter ones are detailed maps of junction-to-ambient heat-conduction path and provide a very wide range of applications of the T3Ster equipment.
The control & evaluation software of T3Ster provides an easy way to compare results of measurements made on different packages: a multitude of the functions can be displayed and investigated at a time – such as shown in Figure 2-6.
Figure 2-4:Temperature response recorded by T3Ster
Figure 2-5:Enlarged part of the response
Figure 2-6: Different functions on the screen (thermal response and its 1st
derivative, time-constant spectrum and the differential structure function)