Voltage/current Spike Averaging Circuit

averaging circuit

I'm currently designing a circuit that will be used as a signal conditioner for a data-logger. It will be measuring the current consumption of a battery powered device. I plan to use a 4ohm resistor to convert the current into about 100mV (at 25mA) and then amplify with an opamp.

Thats all OK, heres the problem:
The device switches on/off a radio chip that uses 25mA. It uses about 10uA when it's turned off. It turns on for 100us; the sample period of the data-logger is 500us! Obviously the data-logger could completely miss the spike! What I would like to do is build some form of averaging circuit so that the spike will always be captured (maybe in 2 samples) so I am still able to work out the energy consumed by the device.

Does anyone have any ideas or calculations that I should be following?

thanks

current spike

I am not sure if I got all your requirements exactly. Nevertheless, my question:
Did you consider already a kind of MEDIAN filter ?
That´s a nonlinear device which is able to cancel impulsive noise spikes without influencing signal edges (which normally is the price for low pass filtering) ?

analog voltage averaging circuits

I understand, that want to measure the true average current rather than the peak current. In this case,a simple low pass would help.

canceling spikes in signals

My requirements are to measure the total power consumption over a long period of time.

A median filter looks like it will completely remove the spike which is not what i actually want to do.

FvM - I agree, a low pass filter may be the best option - I would need to ensure that the spike was flattened only to a level where I can measure it at a low sample rate. For each sample I would be able to work out the average power consumption over that sample period.

Do you have any idea how I would calculate the cutoff of an RC?

voltage spike measurement circuit

The minimum time constant depends on the acceptable error in average current measurement. You can calculate it exactly from the low pass pulse response. For a first order low pass, the maximum error is equal to the ratio of sampling period and time constant in a rough estimation, 5 ms gives 10% and 50 ms 1 % maximum error with 500 us sampling period. If you dont need a specific time resolution, first order should be O.K.