Keithley 4434 Maximize Accuracy free download

File name 4434_Maximize_Accuracy.pdf

Selecting Telecommunication Test Equipment To Maximize Throughput and Accuracy By Robert Green Keithley Instruments, Inc. Soaring demand for cell phones, pagers mobile radios and base-stations, is putting pressure on test engineers to shorten production test time. This may require selection of new test equipment that can improve throughput and accuracy in several areas, including a wide variety of DC and low-frequency board-level tests, and battery testing or simulation. Battery Characteristics To test portable communication devices under realistic conditions, you may need a power supply that can simulate a battery under various discharge states. This requires a power supply with a variable output impedance, which closely duplicates the voltage characteristics of a battery during energy drain. These power supplies should also have an ultra-wide bandwidth output stage to minimize transient voltage droop and recovery time to allow end-of-life rechargeable battery testing. In addition to accurate battery simulation, it is very helpful to have a read-back power supply that can accurately measure load currents. This eliminates the need for a separate instrument and calculation of dynamic power consumption for comparison to test specs. The Keithley Instruments Models 2302 and 2306 are typical of this new breed of power supply specifically designed for portable telecommunication product testing. The 2306 even has a second channel that allows seamless transfer of power from the units battery channel to its charger channel while keeping the device under test (DUT) powered. This allows accurate simulation of a DUTs battery/power supply circuit as it switches to the charger when battery voltage is low, thereby allowing realistic testing of the DUT under these conditions. Switching Systems for Board Testing The principal board-level tests on wireless devices are internal voltages, current drains and power consumption. To speed up multiple measurements, a typical test configuration includes automated signal routing equipment that ties different instruments to several points on the DUT. However, the test system designer must balance throughput and accuracy by selecting the appropriate switching system. Figure 1. Simplified diagram of a cell phone test system using a matrix switch configuration. (A multiplexer topology also could be used; see text.) When you consider the number of signal connections made through the switching system (Figure 1), it becomes apparent that switching consumes a major portion of test cycle time. Several design factors affect switching time: Switch Configurations The current trend in switching system designs is to use one or two basic topologies. The most common ones are the 1 x m multiplexer and the n x m matrix, where the number of inputs, n, is switched to any one of the m outputs. Multiplexer designs are easiest to construct