DESIGN | Angler Circuits

Why do we need a power profiler tool?

The power consumption of IOT devices follow a peculiar pattern which is difficult to measure using traditional equipment. The main reasons for this are listed below

HIGH DYNAMIC RANGE

An IOT device would consume few uA in sleep state and few hundred mA in its transmit state depending on the radio.

Thus the current waveform has a very high dynamic range spanning almost 6 decades.

HIGH BANDWIDTH

The current drawn by the device can change from few mA to 100s of mA in couple of micro seconds. Thus the frequency content of these current waveform is well over few 100KHz.

LONG PROFILE TIMES

It is not uncommon for IOT devices to have a typical profile which can last for several 10s of minutes to 1 hour. They may perform intermittent wake-ups during this time for some misc activities and hence these also need to be recorded. For accurate power analysis, complete capture of the profile is needed.

AVAILABLE OPTIONS

A) Multi-meter with digitizer option

B) Oscilloscope with some current probe

A) Most multimeters use range switching to achieve high dynamic range. While measuring the current, they introduce series resistor and measure the voltage across it. While measuring uA currents, the multimeter would add a few Ohms (may be KOhms) of resistance in series. If the IOT devices performs a wake-up during this state, the drop across the high resistor will cause the device to trip and cause system reset. Most multi-meters made for this application can record profiles for only few minutes. An IOT current profile can last several 10s of minutes and hence the software on the IOT device may need to be modified to account for the limited capture time. Also most multi-meters do not have a full function GUI to measure various pulse parameters. The multi-meters with digitizer options are expensive and retail for about 5K$ and above.

B) Using a scope with a current probe is good enough to measure higher currents in idle and transmission modes. The sleep currents which are of the order of few uA cannot be measured with this due to the limited dynamic range. It can either measure high currents or low currents at a time. Most scopes use a 8 to 12 bit ADC and this limits the overall dynamic range. The capture length limits apply to most scopes and the overall solution is very expensive (At least few K$ for the probe and few 10K$ for the scope)

THE BEST SOLUTION

The best possible solution is to build a dedicated power profiler tool, customized for this application. This need led to the development of the ZS-2102-A IOT Power Profiler featuring the following

Simple connection and GUI
Compact size saving valuable desk space
Low Cost : Can be deployed at each developers desk
Versatile usage
- Hardware engineers
  - Optimize the battery capacity, the battery type
  - Estimate the best value of bulk decoupling capacitor
  - Measure Current profile
  - Debug unexpected peak current and battery drain
- Software engineer
  - Optimize application software to get the best battery life.
No learning curve involved in using this tool. Just plug and measure.

Compact Solution

Easy Interface

Simple setup

Clutter free desk

WHY THE ZS-2102-A BEATS THE COMPETITION?
There are many competing products in the market, specifically designed to measure IOT current profiles. Many of them are excellent in specifications and features. There are some features which makes the ZS-2102-A stand out among the competition.

FAST RESPONSE TIME
Other products perform a slow sampling to improve the overall dynamic range. These can be as slow as 1Ksps with bandwidth of few 100 Hz. Such sluggish response is not good enough for measuring and profiling IOT currents which can change in few micro seconds. The ZS-2102-A has a large signal bandwidth of 300KHz with a 1MSPS sampling which enables a 2uS step response. Such fast response enables to detect short pulses and spikes which can drain the batteries much faster than expected.

HIGH ACCURACY
The measurements are accurate to within 1% of the measured value +/-1uA . This is true across the entire measurement range. The equipment comes with an auto calibration feature which does not require any external calibraiton standards to achieve this performance.

LOW NOISE PERFORMANCE
Fully differential design eliminates common mode noise and provides a clean current waveform. Solutions using an oscilloscope can never achieve the noise performance of the ZS-2102-A.

CONSTANT RESISTANCE
The ZS-2102-A uses a single constant resistance of 100 mOhm across the entire range spanning few uA to 1A. This provides a stable voltage to the load and prevents tripping which is possible with relay switched shunts. MOSFET switched resistors are fast but they can introduce switching noise which is indistinguishable from the load current. Many circuits like LDOs, DCDC converters can become unstable if the series resistance at the input is very high. This can cause system level problems during measurement with switched shunt meters.

EXCELLENT LINEARITY
Use of high speed differential drivers for the ADC with excellent linearity enables the ZS-2102-A to achieve better than 0.1% linearity from few uA to 1A.

NEGATIVE CURRENT MEASUREMENT
The ZS-2102-A operates in two quadrants. (V+,I+) and(V+,I-). While measuring sleep currents, the inherent noise in the system can make the currents go negative. If this is not accounted for, the overall average current would appear higher than the actual value. In case of re-chargeable batteries with solar cells, the measurement of negative current helps to estimate the overall battery life. This is not possible in case of systems which can measure only in one Quadrant.

STANDALONE SOLUTION
Some of the solutions out in the market need a high speed oscilloscope in addition to the measurement probes. This makes it an expensive and very bulky solution. These high speed scopes also have limited sample storage memory.Most of the scopes have limited dynamic range (8 to 12 bits) and therefore cannot measure the sleep currents which are few uA in magnitude. It can either measure high currents or low currents accurately. The high dynamic range of the ZS-2102-A corresponds to more than 24bits which makes measurements from few uA to 1A possible in a single range. The IOT Power Profiler is completely standalone and it needs only a PC to operate. The samples are stored directly on the PC and the capture length is limited by the HDD space alone. With state of the art proprietary data compression, a 1 hour capture can be stored in less than 1GB of storage. All these features of speed, accuracy, dynamic range and long capture time makes the ZS2102A a unique product in its class.

ACTUAL BATTERY MODEL & PROFILE
The ZS-2102-A is able to calculate the de-rating of the capacity of the battery caused by large spike loads, in-sufficient battery recovery time and negative currents. Using this battery model, a better estimate of the battery life can be provided. Competition products only compute the average current and divide the battery capacity in mAh with the average. This is not an accurate method of calculation as it does not take into consideration, the peak to average ratio of the current consumption.

FREE GUI SOFTWARE UPDATES
All the future software updates for the ZS-2102-A would be free for all users.

Electrical Design

The design features low noise techniques to get the best possible performance from the analog components.
It uses fully differential techniques to keep interference and noise coupling to a minimum.
All the analog circuits are simulated across temperature and voltage variations to ensure stability and robustness.
The mixed signal design is carefully laid out to minimize noise and distortion, thereby providing maximum performance.
All the digital signals are simulated to reduce cross-talk and optimize signal integrity.
It features a buzzer to provide warnings and state indications.
The product has gone through rigorous test cycles across temperature and voltage conditions to provide a reliable product. The test cycle is actually 3x longer than the design and development cycle.
It is tested for continuous data logging for more than 24 hours with not even a single random sample, sparkle code from the ADC or an error in the USB transaction. The estimated error is less than 1E-12
Each and every product shipped from us is tested for assembly errors, stability, power supply robustness, noise performance, accuracy and functionality to ensure an excellent customer confidence.
The power profiler tool is enclosed in a custom built anodized aluminum casing for better noise reduction and mechanical strength.

Conformance

The product meets the emission norms specified in FCC Part 15B for Class-A devices. It also conforms to the EU standards for RoHS and Product Safety.