Radio-frequency leakage from a signal generator can create practical difficulties in measuring receiver sensitivities particularly if the receiver itself is not well-shielded Additionally, Inaccuracies in attenuation at the microvolt level may result if strong radiation fields exist.
. If proper magnetic shielding is not provided to the main oscillator of the signal generator then there will be the provision of interference due to the radiation from the wires in the system. This Interference will affect the nearby equipment So, the radiation field effects are eliminated by using RF shielding in RF signal generators. Usually, the shield is made with Copper or Aluminum and is fixed over the chassis.
Importance of Shielding in RF Signal Generator:
1. To prevent RF interference between the components 1.e., each section of blocks comprises various components.
2. To prevent the emission of RF energy from any point except the output terminals.
3. To prevent RF emission on the power line RF chokes and capacitors are used.
WORKING OF DIGITAL IC TESTER
A Digital IC tester is an instrument that tests the digital ICs. Manually operated IC tester, the manufacturers will supply the set code chart to test the corresponding IC, which are in the Internal library. IC testers are available as 14-pin, 16-pin, 24-pin, and 40-pin IC testers.
The tester has 16 thumb-wheel switches arranged in two blocks. The switches are to be set according to the manufacturer's test parameter chart. The poles of the thumb wheel switches are connected to the base where we keep the IC under test. Therefore by setting the position of the thumb wheel switches, we can set any test condition to any of the pins of the IC placed over the base. The test code is read out from the display when the IC is tested.
Before testing we have to set the test code according to the chart presented by the manufacturer. The thumb wheel switches have many positions. Each position is a parameter like input inverted input, no connection, CMOS clock, CMOS inverted clock, TTL clock, ground, supply (+ 5 V), and output. Therefore by setting the position of the thumb wheel switches, we can set any test conditions to any of the pins of the IC placed over the base.
The tester has a clock generator that generates the required clock for testing both CMOS and TTL ICs. The clock output is given to thumb wheel switches and also to enable the application of clock pulses appropriately to the correct pin of the IC. The test pattern generator applies the required supply voltages to the pins of the IC under test. The test key works as the initialization of the circuit. Presenting verification can be done by pressing the test key without placing any IC in the base.
The output of the test pattern generator is given to the address generator. The address generator output goes to the multiplexer, which takes the bits from the thumb wheel switches according to the setting and drives a display to show the condition of the IC, in a four-digit display.
WORKING OF LOGIC ANALYSER
The most popular test instrument for troubleshooting digital and microprocessor-based systems is the logic analyzer. Its appearance is similar to CRO but it looks into the activity of the communicating links in a digital system known as interface buses.
This block ensures that the loading on the SUT because of the logic analyzer is minimal, compensates for the deterioration in signal characteristics due to capacitance loading (the capacitance is cable of carrying the high-speed signals for the SUT to the logic analyzer), and ensures a minimum data/qualifier set up time and a zero data/qualifier hold time.
Since the loge analyzers contain finite memory, say "m" words, the memory subsystem will always contain the "m" most recent word d input data.
The trigger controller block on receipt of the qualified trigger signal from the trigger pattern recognizer ensures that required trigger conditions are satisfied before signaling the memory subsystem to stop writing and instructing the Display controller to take over by reading data at a rate governed by the display clock. The data readout is taken up by the display format for appropriate representation on the CRT screen. In order to examine the activity, multiline data processes are required. In modern logic analyzers, the options available for setting up the equipment are displayed as a menu on the screen with a cursor to indicate the next input required. The keyboard is used to enter the information to give the required operating sequence.
The logic analyzers are usually provided with a series of Personality Modules to reconfigure the equipment for a wide range of microprocessors.
A logic trigger oscillator is adequate when the cost is considered and an oscilloscope is readily available. These units may be as simple as four input AND gates for connection to the oscilloscope trigger input and would synchronize the Oscilloscope with the occurrence of a particular parallel work They may also include counters to delay triggering by a sel number of events or shift register comparators to allow bit serial word recognition for triggering. A logic trigger oscillator is adequate when the cost is considered and an oscilloscope is readily available. These have also used AND gates.
WORKING PRINCIPLE OF SPECTRUM ANALYSER
This is the time domain.
Spectrum analyzers used parallel filter banks andswept frequency technique.
In a parallel filter bank analyzer, the frequency range is covered by a series of filters whose central frequencies and bandwidth are so selected that they overlap each other, Basic Spectrum Analyzer: Referring t, the sawtooth generator provides the sawtooth voltage which drives the horizontal axis element of the scope and this sawtooth voltage is the frequency control element of the voltage tuned oscillator. As the oscillator sweeps from fmin to fmax of its frequency band at a linear recurring rate, it beats with the frequency component of is met during its sweep. The frequency component and voltage-tuned oscillator frequency beat together to produce a different frequency, i.e., IF.
