Tham khảo tài liệu 'microsensors, mems and smart devices - gardner varadhan and awadelkarim part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | MEASUREMENT SETUP 343 Figure Block diagram of dual reference and sample analogue mixing circuit sensor and reference oscillators producing some degree of baseline offset. Although the mixing circuit technique will significantly reduce the effects of common mode interference there is always the possibility that interference could compound and therefore increase measurement errors. Another option is to use an envữonmentally isolated precision reference oscillator. As the frequency from this protected reference oscillator will remain fixed the mixed frequencies from the reference and indicator sensor oscillator will not contain frequency contributions from any interfering source Crabb and Lewis 1973 . MEASUREMENT SETUP The vector network analyser and associated calibration techniques make it possible to accurately measure the transmission parameters of the devices under test. The measurement schematic is shown in Figure . The network analyser consists of a synthesized sweeper 10 MHz-40 GHz test setup 45 MHz-40 GHz HP8510B network analyser and a display processor Subramanian 1998 Piscotty 1998 . The sweeper provides the stimulus and the test setup provides signal separation. The display panel of the HP8510B is used to define and conduct various measurements. The system bus is instrumental in controlling various other instruments. The device to be tested is connected between the test Port 1 and Port 2. The point at which the device is connected to the test setup is called the reference plane. All measurements are made with respect to this reference plane. The measurements are expressed in terms of the scattering parameters referred to as s parameters Subramanian 1998 . These describe the signal flow within the network. 5 parameters are defined as ratios and are represented by Sin out. where the subscripts in and out refer to the input and output signal respectively. Figure shows the energy flow in a two-port network. It can be shown that see HP 851 OB
