Noise Measurement Technique
Original Publication Date: 2003-Dec-10
Included in the Prior Art Database: 2003-Dec-10
In all mobile systems the information to be transmitted is modulated onto a carrier wave, which eventually arrives at a demodulator. It does not arrive alone but comes with noise and interference from many sources. Noise Figure (NF) is one of the most important system parameters that characterise the ability of a system to process low-level signals. Automated Test Equipment (ATE) accuracy for NF measurement is affected by external interference and this disclosure portrays a more accurate NF measurement method using a broadband antenna designed into the Device Interface Board (DIB) for sub-assembly or final module test.
Noise Measurement Technique
Disclosed is a method for NF measurement on an ATE for sub-assembly or final module/product test. Noise Figure (NF) or Noise Power testing on any RF ATE is susceptible to Electromagnetic Interference (EMI). This involves costly solutioning through the use of Faraday Cages in the form of screened rooms, wave guides and DIB screening. This disclosure is not limited to just NF testing, it can be applied to any RF receiver tests on IC's or fully assembled products where EMI is a problem.
Depending on test frequency, a microstrip antenna is designed to the same bandwidth (depending on application) as the Device Under Test's (DUT) receiver test frequencies and build into the DUT's test board (or DIB). This is used by the ATE in order to monitor frequency(s) concerned and determine whether external noise is going to affect the final test results. Figure 1 and figure 2 below show block diagrams of the setup.
ATE Measurement setup
Matching circuitry. etc. for antenna
BThis function is built into DIThis function is preformed by ATE
Filter bandwidth determined by current test conditions
aph with unwanted um grtrSpec DSP A/D
frequencies amplitude levels
ATE test setup for receiver measurement (e.g. NF)
Abbreviations used in figure 2: LNA: Low Noise Amplifier LO: Local Oscillator IF AMP: Intermediate Frequency Amplifier A/D: Analogue to Digital Convertor DSP: Digital Signal Processing
Figure 1 shows the disclosed method installed on a test DIB. The antenna is located as close as possible to the DUT to get an accurate measurement of potential interfering signals. The microstrip antenna is manufactured as part of the DIB which also contains the required matching circuitry to feed the signals back into the ATE for measurement.
Figure 2 shows an overall block diagram of the circuitry. The broadband antenna is fed into a LNA and the amplified signal fed to the input of a mixer. The mixer output is down shifted to a suitable IF frequency determined by the receiver test frequency(s) in use which determines the LO setting (if required). The filter bandwidth is also set according to the test frequencies in use and it's output is fed to an IF amplifier. The resulting signals are then converted to digita...