PIC16F636-How to measure sleep current/standby current and transmit current help

[Dankan]

I am working as Design verification Test Engineer......i found it difficult measuring sleep current/transmitt current on a Key FOB which is using PIC16F636 microprossesor......everytime i measure i get 4uA as sleep current and approximate 2.3mA as transmission current.
How i measure is..i select a resistance and put in series with a ground and measure voltage drop across the resistance divide with the resistance?COULD ANYONE tell me where i need to pay intention or if there could be any method....which is much easier to measure sleep/transmission current?i have attached the waveform as shown on screen.Please help me ......i am ready to give all details regarding this problem.Thank you all good friends

 

[KeepItSimpleStupid]

Yipes! I do think it's going to be pretty tough.

I do think you should put together a simple feedback ammeter. The feedback ammeter will have a few mA of a voltage drop. If you can digitize the current, then you can compute he RMS value mathematically for whatever time period you want to use or whatever "one cycle" is.

~2 mA is is really easy. 100 mA is pretty tough when the load is capacitive. And doing a 4 terminal I-V converter at low voltages is even tougher. You could use 9V or lithium coin cells for power and make an ammeter really quickly. Vos and BW is the most important.

I had to make one to measure light intensity. I-V and a TRMS meter and I did a very complex 4-terminal I-V converter with +-10 V biasing and 4 ranges from 100 mA and lower. This was a front-end to a lock-in amplifier.

It looks like your scope can do RMS measurements of the current. Can you position the cursurs to select the regeon?

 

[Dankan]

Thank you so much for answering so promptly......and yes i can position the cursors to select the region.My Scope has RMS,Vavg and Vp-p.My Question again is,....how do i measure the avarage voltage in such typical waveform as seen above on the attachment?BEcause there are ON and OFF time...i just need to avarage the ONS only.DO you know how to calculate the avarage voltage in such typical waveform?anyone PLEASE reply...i am running out of time and i need a help.Thank you again@KeepItSimpleStupid

 

[Mr RB]

Put a large (47uF ?) tantalum cap across your current sense resistor. Then measure the voltage on the 'scope which will be a close enough average to tell you current consumption. You don't need to make it that complicated.

 

[Dankan]

Thank you Mr RB.....could you explain breifly please why put capacitor across the resistor?Thanks

 

[Mr RB]

It's a common technique to measure an "average" current when the voltage across the current sense resistor is in pulses etc.

 

[Dankan]

Thank you MR RB.....i amgoing to make a try on this