The comprehensive spectrum of ATE instrumentation makes it a large capital investment, either through purchasing or through leasing. Therefore, ATE test programs need to be developed quickly. Also, test time per device needs to be minimized, while providing maximum test coverage to maintain high IC quality. Squelch circuits are used to reject signals that are weaker than a threshold level. Signal detect is used to accept incoming signal greater than a predefined threshold as valid data.
A DiseqC circuit on a satellite set-top box LNB interfaces is a discrete component on the satellite dish that blocks all frequency bands except the low frequency video signal. DiSEqC circuits have a programmable threshold to detect incoming signal as a valid video signal or as interference.
The comparator circuit is normally based on a two-terminal operational amplifier. One terminal of the comparator is tied to a programmable voltage source, which provides a threshold voltage for the comparator. When another input terminal is connected to an input voltage higher than the threshold voltage, the comparator output goes HIGH. In the opposite situation, the comparator outputs goes LOW when the input terminal is connected to a voltage lower than the threshold voltage.
The difference between the threshold voltages when measured from the two directions, is called a hysteresis voltage. In general, due to the relative simplicity of comparator design, test and characterization of comparator should be relatively easy. Unfortunately, current ATE test techniques applied to testing and characterization of comparators are relatively awkward and time consuming. Several test techniques are known for comparator testing. Both transition voltages are logged as comparator threshold voltages.
This method requires multiple steps to search for threshold voltages, and is very time consuming. One relatively high input level is chosen to ensure a comparator output measured at HIGH, and one relatively low input level is selected to ensure a comparator output measured at LOW. It is inevitably imprecise and ignores the comparator hysteresis characteristics. A sine wave or square wave can be used as an input to the comparator, instead of a DC voltage.
Since the comparator output will be a square wave under this stimulus, capturing this output is more difficult than measuring a DC voltage. Typically, certain testability is included with the IC design, which uses one output pin to flag comparator output response, when the input sine wave or square wave amplitude exceeds comparator threshold voltage. Otherwise, the pin will stay at LOW. Instead of incrementing and decrementing PMU DC voltage, the sine wave or square wave input amplitude can be varied to search for comparator threshold voltage.
This test method has the same shortcoming as the previous method—i. The comparator output is captured, and its threshold voltage can be calculated from ramp amplitude and output pulse duty cycle. Unfortunately, sourcing an ideal ramp wave from the AWG can be a difficult task in certain circumstances.
This poses a problem when AWG sees large capacitive loads. For better measurement accuracy, typically a low pass filter is required to smooth out the ramp output sourced from AWG the ramp output from AWG without filtering is actually a step-ramp. The fast transition slope between ramps, which is the only high frequency component in the ramp spectrum, makes the output ramp distorted when the low pass filter is applied.
The non-ideal ramp input means test measurement accuracy is questionable. Triangle wave would be a choice for testing comparator without hysteresis, otherwise the threshold voltage cannot be calculated based on triangle wave amplitude and output pulse width.
The present invention relates to an ATE measurement technique for comparator threshold voltage that substantially obviates the disadvantages of the related art. In one aspect of the present invention there is provided a system and a method for testing a comparator that includes generating two triangular waveform segments having the same period and different amplitudes, inputting the two triangular waveform segments into a comparator, receiving an output of the comparator, and calculating threshold voltages of the comparator based on the output.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.
In the drawings:. Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The present invention overcomes the long test time required by conventional ATE setups. The invention uses a triangular wave with varying amplitude between two adjacent triangles as a stimulus to comparator input, as shown in FIG.
As shown in FIG. The waveform is inputted to a comparator , captured by a digital capture circuit , and is analyzed. The comparator output which is squares waves with different pulse width is captured by the digital capture circuit , as noted above. Based on a time difference between the start points of two adjacent output positive edges and two adjacent output negative edges, both positive and negative comparator threshold voltages can be calculated, and thus the hysteresis voltage can be determined.
Thus, the present invention uses triangular wave with varying input amplitude as comparator input. Using a normal triangular wave input for testing comparator with hysteresis references synchronization between the triangular wave input and the comparator output upon digital capture by the circuit The comparator threshold voltage cannot be determined without knowing the exact time when triangular wave reach its peak, dissecting comparator output pulse into two portion and calculating the respective threshold voltage for both LOW to HIGH and HIGH to LOW transitions.
However, if the amplitude of two adjacent triangular wave pulses is varied, as described below, the synchronization issue can be easily addressed. The implementation of the proposed measurement test technique on ATE is also straightforward:.
Step 2: Create two triangular waves with same period but different amplitude. The up and down ramp should be the symmetric with DC averaged at 0V non-zero DC inputs could distort the baseline of comparator input. Slow ramp triangular wave and appropriate low pass filter is recommended for better input waveform resolution and measurement accuracy.
Step 3: Capture the output of the comparator An ATE digital capture or error map can be used to capture the comparator output. Two triangular wave periods of capture are required. Step 4: Calculate the threshold voltages and log them. The threshold voltages can be calculated based on the equations above. An exemplary portion of C code used for threshold voltage measurement is shown below:. The present invention overcomes the problem of long test time and poor measurement accuracies of conventional comparator test techniques.
Compared to using DC and sine wave inputs, the proposed technique can obtain all threshold voltages and hysteresis while using a single pattern run, and no threshold voltage search is required. Therefore, production test time is considerably reduced. For a comparator with programmable threshold settings, measuring the threshold voltages at all settings can be done in a single pattern run.
Since a triangular waveform is used instead of a ramp, the ringing and uncertainty in transitions due to the ramp fast slope are eliminated, and better measurement accuracy can be achieved. The triangular waveform also combines both positive ramp and negative ramp in one single waveform, and is faster than ramp method, which would require at least two pattern runs to measure positive and negative transition voltage. The triangular wave technique provides better measurement accuracy than the ramp test technique.
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Figure 2. Undervoltage and overvoltage lockout using a single resistive divider. In Figure 1, if the power supply rises slowly and has noise or if the supply has inherent resistance as in a battery that causes the voltage to drop with load current, the output of the comparator will switch high and low repeatedly as the input crosses its UVLO threshold.
For battery-powered circuits, this can be a never-ending oscillation. Using a comparator with hysteresis eliminates this chatter, making the switch transition smoother. If the noise or the drop at the supply input is below this hysteresis, the chatter is eliminated.
There are ways to add or increase hysteresis if that provided by the comparator is either absent or insufficient. All these methods use positive feedback at the divider tap—for example, a rising comparator input jumps higher when the comparator trips. For simplicity, the following equations assume no intrinsic hysteresis in the comparator. Figure 3. Adding undervoltage lockout threshold hysteresis with a resistor from the divider tap to the power switch output. Assume that the switch output is at 0 V due to the system load.
Hence, R H is in parallel with R B for input threshold calculation. The switch turns on above this threshold, connecting the supply to the system. If the comparator itself had some hysteresis, substitute V T with the rising or falling comparator threshold in the previous equations. This method does not work for OVLO because a rising input turns off the power switch, causing R H to pull the comparator input lower which turns on the switch again instead of higher.
Another method of adding hysteresis is to switch in a resistor that changes the effective value of the bottom resistor. The switched resistor can be in parallel Figure 4a or in series Figure 4b. Once V IN is above this threshold, the comparator output is low, turning off M1 and disconnecting R H from the divider. This and the following methods can be used for either undervoltage or overvoltage lockout as their purpose depends on how the comparator output turns on the power switch not shown.
Figure 4. Adding undervoltage or overvoltage lockout threshold hysteresis with a switched a shunt resistor or current and b a series resistor. This shows that the Figure 4b configuration needs a much smaller R H to yield a much larger hysteresis. At the rising input threshold, the negative input of the comparator is at V T.
The previous equations have assumed that the input bias current of the comparator input is zero while the examples have only considered resistor ratios instead of absolute values. Another method is to compare the leakage induced threshold error to that from the offset voltage.
To set up an 11 V input undervoltage threshold with a 0. The divider bias current at the trip point is 0. Resistive dividers enable easy adjustment of power supply undervoltage and overvoltage lockout thresholds with the same comparator-based control circuit. Supply noise or resistance requires threshold hysteresis to prevent power switch on and off chattering as the supply crosses the threshold.
A few different methods for implementing undervoltage and overvoltage lockout hysteresis have been shown.
Hello, I did not save it, but they are very rough, and most of them were done based on experience. Hello, i dont understand the question. Hello Karthick, The circuit is comparing 2 signals with different levels to compare hysteresis. Thanks for walking through the design. I am wondering if your comparator is clocked — because for plotting the hysteresis, I assumed for a clocked comparator, your output OUT should be also swinging rail-to-rail bounded by your power supply.
Here, instead, I see a constant output voltage at 1. Having systematic offset makes the circuit much more sensitive for process spread. Hi, Thank you for a detailed explanation of the working of the circuit. I am trying to solve it though. Could you please tell me other circuits where I could apply this? It is for my project and it needs some innovation. I wish to carry this work further and maybe integrate it in some application. Thanks in advance.
We offer professionally produced videos at affordable prices. Your email address will not be published. About me Contact Suscribe. Skip to content Skip to primary sidebar Skip to footer. Are you Lost? What is the function of hysteresis in a comparator? The hysteresis is essential to compare noisy signals or similar voltages. The schematic The proposed circuit is based on a two-stages open-loop comparator, but adding an internal positive feedback to accomplish the hysteresis.
The basic topology can be seen in the schema: Hysteresis comparator The following 2 schematics are implemented in Cadence. The bias current is set to 80nA. The technology used in this case is TSMC nm general purpose. Test Bench To see several hysteresis, I will sweep different transistor ratio between the positive and negative feedback.
That can be done in Cadence!! Douglas R. Holberg, Phillip E. No spam. I promise. I appreciate your correction. Hi Sir, At what points of Vout, you are calculating the two thresholds?? Asked 6 years, 3 months ago. Modified 6 years, 3 months ago. Viewed 3k times. Imagine using a pull-up resistor to Vcc for a Schmitt trigger in an open-collector output comparator such as: Would the hysteresis calculation include this pull-up resistor R3?
Community Bot 1. Add a comment. Sorted by: Reset to default. Highest score default Date modified newest first Date created oldest first. Michael Karas Michael Karas Is there a practical ratio? The ratio of or more leads to the pullup contribution being quite small. On the other hand you could simply throw it in as a feedback of K or That would really only be applicable to the most exacting calculations in a precision circuit with very accurate temperature stable resistors and a comparator with a very very low differential offset voltage range.
Would that be also times greater than R3 not to effect hysteresis? Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.
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|Campbell newman 4 pillars of investing||An example of such means may include a removable memory chip such as an EPROM, or PROM and associated socket, or other removable storage units and interfaces which allow software and data to be transferred from the removable storage unit to computer system Rogers Germany GmbH. Dynamic hysteresis is hysteresis that does not persist. The up and down ramp should be the symmetric with DC averaged at 0V non-zero DC inputs could distort the baseline of comparator input. Sign up using Email and Password. Right to withdraw consent I am aware that I can withdraw this consent at any time with future effect. If I no longer wish to receive individual newsletters to which I have subscribed, I can also click on the unsubscribe link at the investing comparator hysteresis equation of a newsletter.|
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|Usd forex forecast||Please note that comparator falls under non-linear applications of ICs. The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. VOUT can be calculated with Equation 4 :. In the opposite situation, the comparator outputs goes LOW when the input terminal is connected to a voltage lower than the threshold voltage. Next Page.|
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A comparator is an electronics circuit which compares the voltage of a signal to a voltage reference. If the signal's voltage is greater than the reference, the the output of the comparator swings to the top rail, and likewise if it is less than, it swings to the bottom rail.
Comparators are useful in converting analog signals into square digital signals. With hysteresis a comparator has two voltage thresholds: a high threshold when the output is low, and a low threshold when the output is high. If the output is currently low, then the input voltage must swing above the high threshold, which is higher than the reference voltage, to make the output swing high.
Likewise, when the output is high, the input voltage must swing below the low threshold, to make the output swing to the low rail. A popular comparator is the LM which contains 4 comparators in a 14 pin package. The LM contains 2 comparators. The TL contains a single comparator. Hysteresis can be designed into a comparator circuit, by inserting a resistor from the output to the positive terminal of the comparator.
Computing the resistor values for a given high and low threshold voltage is a common engineering task when dealing with comparators. The general expression for the reference voltage V R in terms of the output voltage, input voltage and resistors is as follows:.
This site uses Google Analytics to track visits. Privacy Statement. You are here: Electronics » Resistor Networks. The Comparator Network Search Tool is used to find a set of resistor values in an inverting comparator circuit that provides the required switching threshold voltage and hysteresis. The reverse can also be performed, finding threshold and hysteresis voltages based on known resistor values. The application can be started using Java Web Start by clicking the Launch button below.
Alternatively, a executable Jar file can be downloaded using the link above. The inverting comparator circuit analysed by the search tool is shown in the left-hand figure below. The feedback resistor provides hysteresis to the switching threshold voltages. The right-hand image below shows how the output voltage changes when the input crosses the switching thresholds. The image below shows the importance of using a comparator circuit with some input hysteresis.
The example is cleaning up a noisy waveform into a binary output signal. The input voltage waveform is shown in the lower blue waveform. The output of a simple comparator without any threshold hysteresis is shown in the top red waveform.
A comparator circuit compares two voltages and outputs either a 1 (the voltage at the plus side; VDD in the illustration) or a 0 (the voltage at the. Ordinary hysteresis is persistent- once the comparator switches, the threshold changes to the new threshold for all time. Figure 1 shows an undervoltage lockout circuit (without hysteresis for now). It has a comparator with a positive reference voltage (VT) at.