In the mobile phone market, mobile phone battery life is a technical indicator that any customer can easily assess. Insufficient battery life can lead to user dissatisfaction. Therefore, extending battery life by reducing power consumption is an important design consideration when designing mobile phones and their key components.
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But the current trend is in the opposite direction: the function of mobile phones is increasing. Internet access, audio, video, and multi-mode capabilities with voice and data are now included, all of which increase battery consumption and reduce uptime. To meet market requirements, mobile phone designers have developed handsets that support a wide range of capabilities and standards, including GSM, CDÎœA, Wi-Fi, HSDPA, WCDÎœA, etc. on a single handset. The function is increased, so that the required driving power is also increased, and power is consumed even if some functions are not operated.
In earlier mobile phone designs, power consumption was primarily determined by RF power amplifiers, microprocessors, backlights, and displays. Designers have made a number of efforts on these subsystems to reduce power consumption, reducing the absolute power consumption during operation to the smallest possible extent. Although the battery is constantly improving, it can't keep up with development requirements. To make phones smaller, thinner, and lighter, battery packs that are smaller in size and weight are needed, and to meet the requirements of larger displays, more features, and longer battery life.
In order to meet these requirements, in addition to tapping into potential in traditional areas, mobile phone designers must also reduce power consumption as much as possible. Today, mobile phone designers have turned to dynamic power usage that can significantly reduce power consumption. With this new power-saving technology, the subsystems in the phone will be turned on or off as needed.
But these subsystems are always connected to the phone's internal power line, which can leak power even when disabled. In order to support many RF standards and the functions users need, the number of these subsystems is still rising. Although each subsystem consumes very little power when it is disabled, it adds up to a considerable amount of power from the battery. Modern handsets use 20 different levels of voltage regulators to optimize the performance and power consumption of each subsystem. And the numerous levels make the problem even worse.
In the R&D lab, engineers need to make a lot of hard work to make changes to the phone's hardware and software to minimize current leakage and optimize battery life, even if the changes are usually very small. They must accurately estimate the total current consumption of the phone in the lab and understand the impact on the overall design of the design by independently measuring the current at the turn-on or turn-off of each subsystem.
Current popular solutions
Although most of the power supplies used to power your phone during testing have built-in current measurement capabilities, these measurements may not be accurate enough. If the power supply is not capable of μA-level current measurement, the ATE system designer will switch to a digital multimeter. But when using a digital multimeter to measure μA current, the power path goes from the power supply to the DUT through the digital multimeter. This increases the complexity and noise of the wiring. When multiple DUTs need to be tested in parallel, using a digital multimeter means adding multiplexers and increasing test time to wait for the switch to stabilize and measure multiple DUTs in sequence. To increase system throughput, a digital multimeter can be assigned to each DUT, which naturally increases costs and adds complexity.
Another way to measure these dynamic currents is to use a dedicated power supply that can only be supplied by a handful of ATE vendors that use high-bandwidth voltage regulators and integrated digital current measurement systems that measure a wide range of currents. When the test is used to replace the mobile phone battery, the power supply can measure the current flowing into the mobile phone during the test, directly giving the power consumption of the mobile phone and the leakage current. Mobile phone manufacturers use this type of dedicated power supply to verify that the mobile phone is capable of meeting power requirements during production testing. This type of dedicated power supply can also be used in the lab to characterize the phone and its key components.
In mobile phone production, most manufacturers measure various operating conditions of the phone, such as large currents when sending, receiving, playing, and accessing the Internet, and small currents during shutdown or standby. High current measurements maintain the fast throughput of the ATE system, but measuring small currents is generally slower because the standby mode, sleep mode, and leakage current measurements require a long integration period to eliminate noise.
It should be noted that the handset switches between high current leakage (such as during a pulse) and low current leakage (such as when on standby). This requires the power supply to behave like a cell phone's battery, and the power supply must have a fast transient response to ensure voltage stability. If the power supply fluctuates against the power supply voltage of the mobile phone during transient changes, the low battery voltage detection circuit of the mobile phone may turn off the mobile phone.
To accurately measure very low currents flowing from the battery, these power supplies have high-resistance current shunts (100Ω to 10kΩ). Uncorrected large shunt resistors can cause very large drops in the output voltage and instability caused by common capacitive loads in the DUT bypass network. To this end, these power supplies must be shorted by dedicated circuits to short-circuit these high-resistance shunts to improve the transient response of the power supply to an acceptable level. Numerous dedicated power supply manufacturers have their own technology, many of which are protected by patents.
Inadequacies in current solutions
In this type of technology, in order to solve the stability problem, a large capacitor is often connected to a high-resistance shunt. Although this solves the voltage stability problem, it wastes a lot of measurement time. The combination of a large resistor and a large capacitor forms a high time constant and a longer settling time when a small current flows through these large resistance shunts.
In addition, these technologies use MOSFETs to connect large resistors to short-circuit resistors and capacitors when driven at high currents. Exciting these FETs creates a discontinuity in the output voltage, which is an insurmountable challenge and not all manufacturers' products will succeed.
Most of the solutions use these technologies to provide sufficient performance for the final test of the mobile phone, but the measurement speed and the dynamic measurement range are not enough to measure the various components in the mobile phone. The current test of the mobile phone production test system usually requires 30μA measurement accuracy within 100ms. But this is too slow and too inaccurate for testing semiconductor devices in mobile phones. Semiconductor devices require faster testing and much lower operating currents. Many devices even require sub-μA-level measurement accuracy and tens of milliseconds of measurement speed.
Patented technology for low current measurement
To measure these low-level currents faster and more accurately, Agilent designers clearly understand that it is impossible to meet end-user requirements simply by developing these technologies. There is now a new precision measurement low current method based on Agilent's patented technology. The patented Agilent power supply provides fast transient response at high currents and enables fast and accurate low level current measurements. This power supply enables faster, low current measurements because it does not require waiting for internal large capacitor charging and signal stabilization. The μA level current measurement can be completed in a few milliseconds with less than 100nA error. For currents greater than 2A, the transient response time is less than 50μs.
Agilent's patented solution uses an active method that removes the capacitors in the current solution that are connected to the high current shunt. Although there are no capacitors, this active method still solves the instability problem caused by large resistance shunts. Without a capacitor, faster response times are achieved. The patented circuit uses an operational amplifier to reduce the resistance of a large value shunt (usually 10kΩ or higher) in the power supply output path to only a few mΩ. If the current flowing through the op amp exceeds the maximum threshold, it turns on a set of MOSFETs that allow a higher current to flow through the large value shunt. The on and off of these MOSFETs are done in a seamless manner without any voltage discontinuities. This technology allows for faster low-level current measurements while retaining excellent transient response for today's dynamic loads.
Application areas of patent solutions
Mobile phone manufacturers can use this solution in production test systems to accurately measure overall machine power consumption in standby mode. Mobile phone component manufacturers such as microprocessors, RF power amplifiers and other related circuit manufacturers can also use this solution in their production test systems. By quickly measuring low currents with a power supply, manufacturing test systems eliminates the need to wait for current measurements, thereby increasing the throughput of the test system. When characterizing the power amplifier transmit characteristics of a handset, throughput is critical to maximizing the use of expensive RF test resources. Equipment footprint is also an important factor for both machine and component production lines. High throughput and small equipment sizes facilitate efficient use of existing plant space, conveyor belts and RF test equipment.
These new measurement techniques have been adopted by the DC output module of the Agilent N6700 modular power supply (Figure 1). R&D and production line engineers can configure a 1-4 output DC power system by selecting 22 DC output modules with different power, voltage and performance levels.
Figure 1: The IU height of the Agilent N6700 modular power supply is ideal for automated test systems.
Agilent offers the N6705A DC Source Analyzer for R&D applications (Figure 2), a new test instrument that integrates four power supplies, a digital multimeter, a high-power arbitrary waveform generator, an oscilloscope, and a data logger into one instrument. Medium is also suitable for use on the workbench. The DC Source Analyzer has a full-featured and user-friendly interface that allows for quick setup testing without programming. For manufacturing, the Agilent N6700 1U highly modular power system provides ATE system designers with the flexibility to optimize performance, power and price to meet production line testing needs. The N6700 modular power system has 400W-1200W three mainframes, and can pack 4 modules in a 1U height chassis to maximize the density of DC power.
Figure 2: Agilent N6705A DC Source Analyzer tailored for R&D engineers.
When using a module with an optional 1UA μA class current measurement system in the N6700 Modular Power System host, the measurement features include integral μA current measurement through its built-in ammeter and data capture using a 50kHz digitizer 4096 point buffer.
When the N6705A DC Source Analyzer is installed in a power module with Option 1UA, the μA-level current measurement system captures current using the DC Source Analyzer's built-in ammeter, oscilloscope, and data logger functions.
In addition to measuring low current, Option 1UA adds mechanical relays to disconnect the positive and negative sides of the power supply, including the remote sensing line, for complete electrical isolation between the power supply and the device under test.
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