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Re: Measuring power consumption of logic gates
Those logic devices that use built-in models as a core do NOT model power supply behavior. This includes current draw, even in the presence of finite output loads.
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Jim Wagner Oregon Research Electronics ----- Original Message -----
From: "matt longbrake" <matt.longbrake@...> To: LTspice@... Sent: Thursday, April 18, 2013 2:14:06 PM Subject: [LTspice] Measuring power consumption of logic gates My question is specifically referring to the 74LVC1G57 found in the LTspice group library, but I think it applies to any digital logic device modeled with the built-in LTspice logic gates. How do you measure the power consumption of a gate as seen by the voltage supply? The supply pin does not actually connect to anything inside the gate model, so as far as the simulation is concerned the supply is sourcing zero current. As an example, I built a simple inverter driving an RC load. The supply was set at 5V and the input signal was a PULSE source generating a clock signal. You can plot the output voltage and see the capacitor charge and discharge. You can plot the gate output current and see it source and sink current to charge and discharge the capacitor. But if you plot the current from the supply it measures 0A. I have built a much more complex circuit and am trying to measure both the peak and average power the supply needs to provide. Is there any way to make the current used by the logic gate be included in the supply current? [Non-text portions of this message have been removed] |
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Re: AD623
David W. Schultz <david.schultz@...> wrote:
You are claiming that a plot of common mode input voltage versus outputYou are correct. My mistake! I was looking at the latest Figure 21, slightly different than the one you are referring to, but they do both refer to the Common Mode Input voltage. Figure 22 does show that the AD623 does NOT tolerate the simultaneous condition of having the output at around +2.5V, with the inputs near ground. This fact is ignored by a reading of the amp's features on page 1, where it implies that the inputs can go 150 mV below ground ... without saying anything about the conditions that allow that much input voltage range. Based on Figure 22, I'd say the original questioner (Xinjun) cannot do what he is trying to do with an AD623 in this circuit. Either design the circuit differently, or use something other than the AD623. Andy |
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Measuring power consumption of logic gates
My question is specifically referring to the 74LVC1G57 found in the LTspice group library, but I think it applies to any digital logic device modeled with the built-in LTspice logic gates.
How do you measure the power consumption of a gate as seen by the voltage supply? The supply pin does not actually connect to anything inside the gate model, so as far as the simulation is concerned the supply is sourcing zero current. As an example, I built a simple inverter driving an RC load. The supply was set at 5V and the input signal was a PULSE source generating a clock signal. You can plot the output voltage and see the capacitor charge and discharge. You can plot the gate output current and see it source and sink current to charge and discharge the capacitor. But if you plot the current from the supply it measures 0A. I have built a much more complex circuit and am trying to measure both the peak and average power the supply needs to provide. Is there any way to make the current used by the logic gate be included in the supply current? |
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Re: LTC2377
--- In LTspice@..., Andy <Andrew.Ingraham@...> wrote:
I think Helmut asked a very good question and I'm sure he knows what IBIS is.I am well aware Helmut knows what IBIS is. He has helped answer other Hello Andy, I have asked Mike a few times to to enhance LTspice with an IBIS translator, but he didn't like to spend time and money for that. "It's easier for a camel to go through the eye of a needle." before we will get IBIS In LTspice. I would be happy if anybody will write a translator. Some tried in the past (even I), but I gave up because it's too much effort beyond my other activities. Best regards, Helmut |
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Re: AD623
On 04/18/2013 03:19 PM, Andy wrote:
Figure 21 applies to the output common-mode voltage, not inputYou are claiming that a plot of common mode input voltage versus output voltage says nothing about common mode input voltage? Surely you must be joking. Or perhaps looking at a different revision of the datasheet than I am. I just grabbed one off the Analog Devices web site and that figure is now Figure 22. "Maximum Output Voltage vs. Common-Mode Input, G=1, Vs=5V, Rl = 100K" -- David W. Schultz Returned for Regrooving |
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Re: LTC2377
I think Helmut asked a very good question and I'm sure he knows what IBIS is.I am well aware Helmut knows what IBIS is. He has helped answer other people's questions about IBIS models. But I got the impression he either didn't catch that this was an IBIS model, or didn't catch that the user had an IBIS model and now wanted to know what to do with it in LTspice. I thought it was a legitimate question, how do I simulate in LTspice using this IBIS model. I didn't think Helmut's answer was on-track with that question, even though it may have been a very good question to ask. Like I say, I may have simply misunderstood Helmut's answer. Andy |
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Re: AD623
--- In LTspice@..., Andy <Andrew.Ingraham@...> wrote:
Hello Andy, please reset your SPICE settings. Control Panel -> SPICE -> Reset to default Best regards, Helmut |
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Re: AD623
David W. Schultz <david.schultz@...> wrote:
The AD623 is an instrumentation amplifier and the gain is set with aThe AD623 data sheet allows (recommends) leaving Rg open. (I questioned that too, until I read the datasheet.) The AD623 amplifies the difference between its input voltages. One ofThe data sheet allows this. The "input range extends 150 mV below ground (single supply)." The applied input signal is within that range. If you look at Figure 21 in the AD623 dataFigure 21 applies to the output common-mode voltage, not input common-mode voltage. The output common-mode voltage in this circuit, set by Vref, is exactly in the middle between +Vs and -Vs. Me, I am not happy with this simulation. Something seems very wrong. I downloaded Helmut's suggested fix and it seems to work, EXCEPT that there is still a strange offset from the desired Vref voltage. I don't get it. Vout should be centered on +2.5V but it isn't. I tried implementing Helmut's suggested fix (1.0 ohm Rser) and it didn't work at all; the voltages "blew up". I downloaded Helmut's other suggested file and the offset from Vref was still there but in the opposite direction! Something very strange seems to be going on here. (Or maybe I am doing something wrong?) Andy |
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Re: LTC2377
--- In LTspice@..., "sawreyrw" <sawreyrw@...> wrote:
Hello Rick, Yes I well know IBIS files. But Elena asked like not be interested in IBIS files. Best regards, Helmut |
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Re: LTC2377
--- In LTspice@..., Andy <Andrew.Ingraham@...> wrote:
Andy,What do you expect from an ADC model in SPICE?Maybe you misunderstood the question, Helmut. Or maybe I I think Helmut asked a very good question and I'm sure he knows what IBIS is. Rick |
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Re: LTC2377
What do you expect from an ADC model in SPICE?Maybe you misunderstood the question, Helmut. Or maybe I misunderstood the answer. Linear Tech. has only an IBIS file for this part, no SPICE model (apparently). LTspice doesn't take IBIS model files. Some other SPICE simulators do. There is a program to convert IBIS model files to SPICE models, but it does not always give usable results. Even so, you need to be aware of what IBIS models are for ... they represent the electrical characteristics of pins and their attached circuitry, but not of the entire IC. Andy |
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Re: AD623
--- In LTspice@..., Jean Pierre Daviau <daviaujp@...> wrote:
Hello, I can't see your uploaded file. Please check that you have really uploaded it. Your mentioned directory doesn't exist anymore. Normally users should upload circuits for discussion to Files > Temp > your_files.zip Best regards, Helmut |
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Re: AD623
On 04/18/2013 01:37 PM, free2rhymedd wrote:
I am new to the LTSPICE. I was trying to shift the input voltage upThe AD623 is an instrumentation amplifier and the gain is set with a resistor between the two Rg pins. While leaving them open should get you a gain of 1, it makes me nervous. At the very least you have to be vary careful about leakage currents between the two open pins. The AD623 amplifies the difference between its input voltages. One of the details that you will find in the data sheet is that it doesn't care for common mode voltages close to the rails. Your circuit has a common mode input voltage of zero. If you look at Figure 21 in the AD623 data sheet you will see that it has a sharply reduced output voltage range under this condition. About 0.5V maximum. If I replace the ground connection on the input with a 2.5V DC source to provide an offset, the output of the AD623 follows the input as expected. (Or replace it with a connection to your 2.5V reference circuit.) Despite its common mode voltage limitations, the AD623 is one of my favorite instrumentation amps. I used it in this project: -- David W. Schultz Returned for Regrooving |
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Re: AD623
Jean Pierre Daviau
No file
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----- Original Message -----
From: free2rhymedd To: LTspice@... Sent: Thursday, April 18, 2013 2:37 PM Subject: [LTspice] AD623 I am new to the LTSPICE. I was trying to shift the input voltage up by 2.5V. I am using AD6232 to shift up the voltage, but it does not work properly. I have uploaded the circuit on the forum. Here is the link: . Hope someone can help me. Thank you. |
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Re: AD623
Hi, Helmut
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Thank you very much. It works now. I appreciate it very much. Xinjun --- In LTspice@..., "Helmut" <helmutsennewald@...> wrote:
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Re: AD623
--- In LTspice@..., "free2rhymedd" <xinjundong@...> wrote:
Hello, I agree that this circuit converged to a wrong DC operating point. I tried different things. Finally I decided to use the solution with only one +5V supply. This has the advantage that it's useful for the .AC simulation too. I have added data labels to see the DC-operating point voltages. This enables you to check that ..AC-simulation has been done in the correct DC-operating point. I just discovered that it has been sufficient to set a 1Ohm series resistance in V1. See L-28_.asc. I have moved your files and added my solutions. Files > Files sorted by message number > msg_66295 Best regards, Helmut |
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