Modification of the LM124 Single Event Transients by Load Resistors
Summary (3 min read)
Introduction
- Sharing similar internal blocks, operational amplifiers are not very different from comparators so it would be interesting to investigate the way that the single event transients are modified by the presence of a resistive load.
- This astonishing result was attributed by the authors to a coupling between the resistance values, gain, and bandwidth.
A. Laser configuration
- The experiments were performed at the UCM Multiphotonic Spectroscopy and Femtosecond Facility using a Ti:Sapphire laser followed by a regenerative amplifier.
- For two-photon absorption processes in silicon, 60-fs laser pulses at a frequency of 1 kHz and a wavelength of 1300 nm was fixed.
- The energy was measured with a typical commercial powermeter and set to 1.2 nJ.
- The device was mounted on a motorized xyz stage with 0.1 µm resolution and it could be observed with an infrared CCD camera to allow the correct placement of the laser.
- Afterwards, a sweep along the z-axis was performed in order to store a large set of output transients and, this way, to statistically validate the results.
B. Electronic set-up
- The LM124 operational amplifier, in quad CERDIP package, was mechanically decapsulated and tested as follows.
- A set of jumpers allowed the selection of the 1%-tolerance resistors with different values to load the operation amplifier output (Fig. 2).
- Finally, the device was biased with ±15 V power supplies.
- The output was connected to a digital oscilloscope with 8- pF probes that was triggered by means of an external signal coming from the laser (Fig. 1).
- Given that the step was 10 ns, every set of data amounted to 10.000 points that were saved by a specific LabView application, which also controlled all the devices by means of the GPIB protocol.
III. RESULTS
- Four points were chosen to investigate the effects of the resistive load on the shape on the laser induced transients.
- Q09 in Fig. 3 is called Q12 at the datasheet by National Semiconductors [12].
- The actual structure has been determined by several authors [7], [8], [10], [19], [20], although there are minor changes among the schematics provided by the different works.
- At each depth value, the data after the laser impact were saved in the hard disk of the computer to be analyzed by a specially developed SCILAB program in order to obtain typical parameters such as the peak voltage, full width-half maximum (FWHM), etc.
- According to the results, there was not a significant difference among the output transients observed after hitting Q18 or Q20.
B. Transients at QR1
- Those transients induced on the base of QR1 are usually short spikes that lead the output voltage up to the positive saturation voltage [8], [9].
- The reason of this transient is that the activation of QR1 takes the whole of the Q09 base current, momentarily cutting this transistor off so the output of the gain stage goes to a high positive value.
- According to these results, it seems clear that the second stage of the transients, where the output voltage is negative, is attenuated as the load resistance decreases.
- First of all, the line corresponding to a 3.3 kΩ resistor is just a short and small spike.
IV. DISCUSSION
- Experimental data show that the load resistance affects the shape of the output transients.
- With the help of the analysis of the output stage and simulations, a theory to explain the distortions and attenuation of the single event transients, and based on the switch of some transistors to anomalous states, will be developed in the following sections.
A. DC behavior of the output stage
- Unlike most of the typical general-purpose operational amplifiers that make use of a class AB output stage, the LM124 output stage is a combination of two emitter followers that cannot simultaneously work.
- The way that the stage operates depends on the value of the output current, IO, (Fig. 11).
- In fact, if the output current is positive or, at least, negative but lower than IBO, Q13 & Q14 must be in forward active zone to accomplish the Kirchoff’s current law at the OUT node.
- Finally, the purpose of Q12 is to protect the device from overcurrent.
- Besides, when the amplifiers does not provide a lot of positive output current, the voltage drop through RSC is very low so the transistor remains in cutoff state.
B. SPICE simulations
- SPICE simulations were performed in order to find out the reasons of the change of the SETs.
- Unfortunately, this technology is not at the authors’ disposal.
- Given that the purpose of the simulations is to broadly understand the behavior of the device, the authors proceeded to do the following approaches:.
- The base resistance was removed of the transistor model and placed outside [22].
- Even after all these simplifications, the results are meaningful.
F. Effects on fed-back operational amplifiers
- Experimental results have shown that a load resistance can affect the characteristics of the single event transients originated at the gain stage.
- Operational amplifiers can have resistive loads in some situations not as clear as that shown in this figure.
- A fast increase after quitting the negative saturation voltage before the recovery accomplishing the slew rate requirement, and the presence of humps when the output value is on the order of −50µA· (R1 + R2).
- Paradoxically, the presence of the hump makes the transient with 10 kΩ a little longer than the others, even though its value of FWHM is clearly lower.
- E. g., Sternberg et al. found that the network resistor values clearly modify the size and shape of the simulated transients [5].
V. CONCLUSION
- Some of the typical transients observed at the output of the LM124 operational amplifiers after a pulsed laser impact are modified by the presence of a resistive load at the output.
- The affected output transients seems to be shorter and smaller than those observed without any resistive load.
- Besides, the distortion depends on the DC output voltage.
- First of all, the current associated with the load resistor helps the internal transistors to recover the original state, and also the output stage cannot instantaneously change its operation point to bias the load resistor.
- Finally, tests on fed-back amplifiers were performed to find out if the resistor values affected the shape of the output transients.
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Citations
13 citations
Cites methods from "Modification of the LM124 Single Ev..."
...The influence of these factors on the ASET responses was investigated in case of voltage feedback amplifier (VFA) as for LM124 [3], [4], [6], [11] and LM139 [7]....
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13 citations
Cites background or methods or result from "Modification of the LM124 Single Ev..."
...In particular, they were used to understand the influence of the load resistors in the shape of the transients [30], [41] and to investigate the long duration pulses observed in linear voltage regulators, either series or shunt [42]–[44], due to peak detector effect....
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...One can find the old simulations in [30], [41] and observe how the ongoing improvement of the models makes the simulations closer to the experimental results....
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...Actual transients in the laser facility (a) and simulation (b) [41]....
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7 citations
Cites methods from "Modification of the LM124 Single Ev..."
...Transient simulations were run with a LM124 SPICE micromodel [9] working in this configuration and injecting a current pulse into Q09 base (Fig....
[...]
...The LM124J was unpackaged and tested working as voltage regulator at the UCM laser facility [9]....
[...]
7 citations
6 citations
Cites background from "Modification of the LM124 Single Ev..."
...The LM124 is a quad part packaged in a 14- pin ceramic dual inline package (CERDIP), whereas the LM119 is a dual part....
[...]
...the ASET sensitivity of both the LM124 [6-10] and the LM119 [11] by monitoring only one of the outputs....
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...Previous publications have reported on the ASET sensitivity of both the LM124 [6-10] and the LM119 [11] by monitoring only one of the outputs....
[...]
...Moreover, when any of the current mirroring transistor from the current source used to transfer the current to the different amplifiers are impacted (the four sensitive areas appearing in black on the left side of the LM124’s current source on Fig....
[...]
...Pulsed laser single event effects (PLSEE) technique was used to test the sensitivity of an operational amplifier (the LM124) and a comparator (the LM119) to multiple-output transient (MOT) (simultaneous analog signal transients induced by a single particle propagating through two different IC output)....
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References
4,717 citations
"Modification of the LM124 Single Ev..." refers background in this paper
...2) Spice parameters were the typical values of a 5 -cm, 17 -epi 44-V technology [ 21 ]....
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252 citations
"Modification of the LM124 Single Ev..." refers background in this paper
...This kind of test could be done since the laser wavelength was chosen to induce two-photon absorption processes, able to induce transients in buried layers of the device [3]....
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123 citations
"Modification of the LM124 Single Ev..." refers background in this paper
...Probably, the reason of this failure is that a unique current source cannot modelate a multi-junction charge collection process [24]....
[...]
80 citations
"Modification of the LM124 Single Ev..." refers background in this paper
...Previous papers have dealt with the influence of the output resistance in comparators showing that there is a clear dependence of the transient shape on the resistance value [1], [13]–[15]....
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79 citations
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Frequently Asked Questions (12)
Q2. What is the trend of the typical single event transients related to this spot?
In the typical single event transients related to this spot, the trend is that small resistance values minimize the size of the transients, in particular during the second period where the output voltage reaches large negative values.
Q3. What are the transients induced on the base of Q09?
Those transients induced on the base of QR1 are usually short spikes that lead the output voltage up to the positive saturation voltage [8], [9].
Q4. What is the way to drain the excess of current towards VEE?
if the output current is negative and higher than IBO, the only way to drain the excess of current towards −VEE is through Q11, a PNP transistor.
Q5. What is the reason for the failure of the transistors?
a careful study of the behavior of the transistors during the transientsallows understanding that the actual reason is that, temporarily, some transistors give up working in the correct mode making the whole device not operating in the typical zone.
Q6. What is the typical configuration of the amplifier?
Let us suppose that the amplifier is in a typical noninverting configuration, with two resistors R1 & R2 in such a way that the gain is 1 + R2/R1.
Q7. What is the reason for the distortion of the transients?
the distortion of the transients related to the change of the load resistance, either pure load or resistive network, are explained supposing a coupling effect.
Q8. What is the z-value of the transients?
Provided that these transients appears in a narrow interval of z-values, it is likely that these events are related to a charge generation near a buried layer.
Q9. What is the reason why the Q09 transients vanish?
Just like the Q09 transients, these humps vanish with appropriated values of input voltage due to the fact that there is no switching among the output stage transistors.
Q10. What is the output current of the Q09 collector?
Given this resistance value and that the value of the output voltage was about –3 V, the output current was −3/47 = −64 µA, a value that accurately fits the forecast output current to make Q12 switch off.
Q11. What is the main reason for the distortion of the LM124 SETs?
As expected, load effects related to the feed-back network are evident so this phenomenon must be taken into account along with the shift of the operational amplifier poles and zeros to explain the distortion of the LM124 SETs.
Q12. What is the typical procedure for separating the individual transistors?
In fact, the typical procedure is separating the individual transistors by means of laser or ion beams and extract the SPICE parameters using a microprobe and specific instrumentation [18].