Tester for RF devices
For testing an RF device, such as an RF receiver/decoder chip that receives an RF signal via an antenna terminal and outputs a digital code at an output terminal, an inexpensive non-RF programmable tester is used. The programmable tester is a commercially available tester that need only generate and receive non-RF digital and analog signals. The RF signals needed for the testing of the RF device are totally supplied by RF generators on a single printed circuit board, external to the commercial tester housing. The board contains controllable RF generating circuitry whose possible output amplitudes and frequencies need be only those necessary for testing the particular DUT. The frequencies may be changed by switching in different crystal resonators mounted on the board.
1. A test system for devices requiring a radio frequency (RF) input signal, the tester comprising:
a programmable test unit, the programmable test unit outputting non-RF control signals and receiving non-RF test signals from a device under test, the programmable test unit being programmable to control a test sequence for determining a performance of the device under test, the device under test having at least one RF input terminal, the programmable test unit having no RF capability and being enclosed in at least one housing;
a circuit board, external to the at least one housing of the programmable test unit, the circuit board having input terminals connected to the programmable test unit for receiving the non-RF control signals and having output terminals connected to the programmable test unit for transmitting non-RF test signals from the device under test to the programmable test unit, the circuit board comprising:
a first controllable RF oscillator connected to receive a first control signal from the programmable test unit, the first controllable RF oscillator being controllable to output a plurality of radio frequencies where the particular RF output is determined by the first control signal;
an RF modulator coupled to receive an RF output of the first controllable RF oscillator and coupled to receive a modulating signal from the programmable test unit, the RF modulator outputting a modulated RF signal at a first amplitude;
a variable attenuator coupled to an output of the RF modulator and coupled to receive a second control signal from the programmable test unit for outputting a plurality of amplitudes of the modulated RF signal;
a power splitter coupled to receive the plurality of amplitudes of the modulated RF signal, the power splitter having a first output terminal outputting a first split modulated RF signal for coupling to a first RF input terminal of the device under test, the power splitter having a second output terminal outputting a second split modulated RF signal;
a detector having an input terminal coupled to receive the second split modulated RF signal, the detector converting the second split modulated RF signal to a DC level corresponding to a power level of the second split modulated RF signal, the detector having an output terminal coupling the DC level to an input terminal of the programmable test unit; and
electrical terminals, configured to be temporarily connected to terminals of the device under test without cabling, to couple the first split modulated RF signal to the first RF input terminal of the device under test, to couple some of the non-RF control signals from the programmable test unit to control input terminals of the device under test, and to couple the non-RF test signals from the device under test to the programmable test unit for evaluation by the programmable test unit of the performance of the device under test in response to the non-RF control signals and the first split modulated RF signal,
wherein no RF cabling is used between the programmable test unit and the circuit board.
2. The system of claim 1 wherein the first controllable RF oscillator comprises a plurality of crystal resonators, a crystal oscillator, a frequency multiplier, and a switch controlled by the first control signal to connect one of the crystal resonators to the crystal oscillator to generate one of a plurality of reference frequencies coupled to the frequency multiplier.
3. The system of claim 1 wherein there is no RF cabling from the board to the device under test.
4. The system of claim 1 wherein the modulating signal from the programmable test unit is connected to the RF modulator to switch the RF output of the first controllable RF oscillator on and off.
5. The system of claim 1 wherein the modulating signal from the programmable test unit is connected to the RF modulator to vary a frequency of the RF output of the first controllable RF oscillator to generate an FM signal.
6. The system of claim 1 wherein the variable attenuator comprises:
a first attenuator having an input coupled to receive the modulated RF output of the RF modulator, the first attenuator being coupled to receive the second control signal and having an output for providing an attenuated modulated RF signal based on a magnitude of the second control signal;
a first RF switch having an input terminal coupled to the output of the first attenuator, the first RF switch having a first output terminal and a second output terminal, wherein a third control signal from the programmable test unit controls the first RF switch to selectively couple its input terminal to the first output terminal or the second output terminal;
a fixed attenuator having an input terminal coupled to the first output terminal of the first RF switch, the fixed attenuator having an output terminal; and
a second RF switch having a first input terminal connected to the second output terminal of the first RF switch and having a second input terminal connected to the output terminal of the fixed attenuator, wherein a fourth control signal from the programmable test unit controls the second RF switch to selectively couple its output terminal to its first input terminal or its second input terminal.
7. The system of claim 6 wherein the third control signal and the fourth control signal are the same signals.
8. The system of claim 1 wherein the electrical terminals for connection to terminals of the device under test comprise a test contactor.
9. The system of claim 1 wherein the device under test is an RF receiver.
10. The system of claim 1 wherein some of the electrical terminals on the board are electrically connected to the programmable test unit for supplying control signals to the device under test to carry out functions performed by the device under test under different RF parameters.