New functions are constantly added to intelligent terminals , Battery life has become one of the most headache problems for users . Compared with portable power supply and cable power supply , Wireless charging technology has received great attention because of its convenience and versatility , So as to become one of the best solutions in the market . As one of the most popular applications of wireless charging technology , Wireless device due to long operation time , Therefore, it is necessary to provide better charging performance .

This guide is for Keysight E4980A/AL precision LCR Table how to characterize the most commonly used components in wireless charging system —— The coil is described .

chart 1. E4980A precision LCR surface

Coil of wireless charging system

There is more than one wireless charging standard in use today , But they have one thing in common , Generally, coils are used ( Or coil based resonators ) To generate electromagnetic fields , And energy transmission . A typical wireless charging system consists of two parts ： Transmitting unit and receiving unit , Power and energy can be transmitted through inductive coupling , Between transmitter and receiver （ chart 2）. Usually , The transmitting coil and the driving circuit are installed on the charging base , The receiving coil and related circuits are placed in the device that needs to be charged , Such as smart phones . Power transmission efficiency is the key index of wireless charging system . This indicator is affected by many factors , For example, the distance between coils , Inductance parasitic , How the coils are arranged, etc . For a single coil , in the majority of cases , Minimum loss is required in the design stage （ low DCR） And parasitism （ high Q）. Typical test parameters of transmitter and receiver coils are Ls（ Series inductance ）,Rs（ Series resistance ） and DCR（ DC resistance ）. be based on WPC The standard coil test frequency is usually lower than 1MHz.

E4980A/AL precision LCR The watch is up to 2 MHz Standard solutions for the measurement industry of components . Because of its high accuracy and repeatable measurement 、 Wide impedance range and high measurement speed are widely favored by the component manufacturing market .

chart 2. Wireless charging system

High precision standard DCR measurement

Transmitter coil and receiver coil DC resistance will directly affect the resistance loss of energy transmission , Therefore, low DCR（ Usually as low as milliohm ） To ensure high power transmission efficiency .

DCR （ DC resistance ） The measurement is E4980A/AL precision LCR The standard function of the meter . E4980A/AL It can measure very accurately as low as milliohm DCR value . meanwhile , E4980A/AL Low contact resistance support fixture , Such as 16047E And fixture compensation function . If the coil DCR yes 100 Milliohm ,E4980A/AL Of DCR The accuracy can be as high as 5%, It means that the true value is about 95 Milliohm to 105 Between milliohms . This accuracy is very high , Because based on the automatic balance bridge method LCR The meter measures low DCR Is very difficult .

Wide impedance range is used to measure inductance and stable small impedance ESR

The inductance of the transmitter and receiver coils is usually in the micro range μH Range , The test is carried out in the frequency range of tens of kHz . therefore , The impedance ranges from a few milliohms to a few ohms .E4980A/AL LCR The meter has excellent performance in a wide impedance range , stay 4 Milliohm to 100 Between milliohms 10% within The accuracy of the （ chart 2）, It is especially suitable for the measurement of coils in wireless charging system .

Equivalent series resistance of inductance （ESR） It also needs to be small and stable , To meet the requirements of low power consumption . E4980A/AL by ESR Measurement provides excellent measurement stability （ chart 3）.

frequency Hertz

chart 2. 10% Impedance measurement accuracy range （ test signal 1Vrms,MED Pattern , cable 0 rice ）

chart 3. Low impedance evaluation （E4980A, 1 Milliohm 100K Hertz ）

Fast measurement , Improve product yield

The main concern of the manufacturing industry is to increase production , Reduce the cost of testing .E4980A/AL It has the function of fast measurement , It improves the measurement efficiency of design and manufacturing .E4980A The measurement speed of is as follows ：

• short （SHORT） In mode ,1 Megahertz per point 5.6 millisecond
• in （MED） In mode ,1 Megahertz per point 88 millisecond
• Long （LONG） In mode ,1 Megahertz per point 220 millisecond

A large number of test fixtures meet the test requirements

E4980A/AL LCR The watch can be matched with more than 20 kinds of fixtures , To meet from materials to SMD Various evaluation requirements for components .16047 Series lead-in fixture is used to measure low DCR and ESR The best fixture for lead-in coil . Besides ,E4980A/AL The built-in compensation function minimizes the impact of the test fixture