Getting time domain current from impedance and voltage measurement?

In summary: The switcher feeds the plane with the BGA contacts. There is an output from the switcher. Is it a buck or multiple bucks? Clamp the output inductors...It could be okay to just divide the values of the frequency components of voltage by the value of the impedance at that frequency, and then perform the inverse transform to get current. This should be done element-wise in the frequency domain and not by using convolution. So, if I were to take the time domain voltage signal source (i.e. a bunch of sinusoidal voltage sources in series) and convert it to the frequency domain, I would multiply each voltage source by the corresponding impedance and then perform the inverse
  • #1
awvvu
188
1
I'm working on a high power multi-phase DC/DC converter where the load current has some fast transients. We can easily measure the output voltage in the time domain, and also measure the power distribution network impedance in the frequency domain.

So, I think I would try converting the time-domain output voltage to frequency-domain, and then do I = V/Z. Now I'm a little confused, because in the frequency domain, does this mean I should convolve V with 1/Z? After getting the frequency-domain current, then I'll convert this back into time-domain with ifft.

Or can anyone suggest any other methods to measure the current using another method? This is possibly in the 0-100A range going through tons of BGA balls so I don't think I can measure it directly.
 
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  • #2
awvvu said:
I'm working on a high power multi-phase DC/DC converter where the load current has some fast transients. We can easily measure the output voltage in the time domain, and also measure the power distribution network impedance in the frequency domain.

So, I think I would try converting the time-domain output voltage to frequency-domain, and then do I = V/Z. Now I'm a little confused, because in the frequency domain, does this mean I should convolve V with 1/Z? After getting the frequency-domain current, then I'll convert this back into time-domain with ifft.

Or can anyone suggest any other methods to measure the current using another method? This is possibly in the 0-100A range going through tons of BGA balls so I don't think I can measure it directly.

I would suggest putting a 0.1 Ohm precision resistor in series with the output of the power supply, and digitizing the differential voltage drop across the resistor along with the input voltage to the resistor. That should give you what you need.
 
  • #3
Can't do that, the power supply is 1V and the load is almost 100A. The power trace is an entire internal plane to minimize I^2 R loss, so I think the only way to measure the current is indirectly.
 
  • #4
awvvu said:
Can't do that, the power supply is 1V and the load is almost 100A. The power trace is an entire internal plane to minimize I^2 R loss, so I think the only way to measure the current is indirectly.

Nope. Next choice is using a Hall Effect current probe:

http://www.industrial-toolz.com/?p=439 [Broken]

Can you rent one of those?
 
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  • #5
Yeah, but I can only measure the input current into the switcher, and that's not useful for getting transient data. The actual load is a BGA chip so I can't use a current probe directly.
 
  • #6
awvvu said:
Yeah, but I can only measure the input current into the switcher, and that's not useful for getting transient data. The actual load is a BGA chip so I can't use a current probe directly.

The switcher feeds the plane with the BGA contacts. There is an output from the switcher. Is it a buck or multiple bucks? Clamp the output inductors...
 
  • #7
It could be okay to just divide the values of the frequency components of voltage by the value of the impedance at that frequency, and then perform the inverse transform to get current. This should be done element-wise in the frequency domain and not by using convolution.

You may think of the time domain voltage signal source as of as a number of sinusoidal voltage sources in series, with amplitude and phase that may be determined by the DFT of the measured voltage. The theoretical time domain current at the input to the network could be found by superposition, by adding the currents through the load from each of the voltage sources.

There are elements for negative frequencies in the vector that results from the FFT, though.

Perhaps something like this:

1. Divide the elements for zero and positive frequencies by the corresponding impedance at that frequency.
2. In the resulting (transformed current) vector, set the elements for negative frequencies equal to the complex conjurgate of the corresponding positive frequency.
3. Perform the inverse transform.
 
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1. How do you measure impedance and voltage?

To measure impedance and voltage, you would need a device called an oscilloscope. This device captures and displays electrical signals over time, allowing you to measure the voltage and impedance of a circuit.

2. What is the relationship between impedance and current?

Impedance is the measure of the opposition to current flow in a circuit. It is a combination of resistance, inductance, and capacitance. The higher the impedance, the lower the current flow.

3. How do you calculate time domain current from impedance and voltage measurements?

To calculate time domain current from impedance and voltage measurements, you can use Ohm's law (I = V/Z) where I is the current, V is the voltage, and Z is the impedance. This formula can be applied to each data point in the time domain to determine the current at that specific moment.

4. What is the importance of measuring time domain current?

Measuring time domain current is important in understanding how the current changes over time in a circuit. This can reveal information about the behavior and health of the circuit, and help in troubleshooting and identifying any issues.

5. Can impedance and voltage measurements be used to predict future current flow?

No, impedance and voltage measurements cannot predict future current flow. These measurements only show the current flow at a specific moment in time and cannot predict how the current will change in the future. Other factors such as circuit components, external factors, and load can also affect the current flow.

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