An improved circuit for phase noise measurements utilizing a frequency down conversion/multiplier and direct spectrum measurement technique which uses a combination of a phase detector method and a direct spectrum approach. The circuit is particularly useful for field test environments where laboratory instrumentation is normally not available, and fast and accurate phase noise measurements are required. The phase noise measuring circuit includes a frequency mixer which has a first input signal from a device under test and a second input signal from a reference stable oscillator having ultra low phase noise with a fixed center frequency. The frequency mixer mixes the first and second input signals to produce a down converted signal comprising the frequency difference signal of the first and second input signals. A lowpass filter then passes the down converted signal to a frequency doubler circuit which produces a doubled frequency, down converted signal. A lowpass signal filter then passes the doubled frequency, down converted signal to an amplifier. The output of the amplifier is directed to a second frequency doubler circuit which produces a quadrupled frequency, down converted signal. That signal is then directed to a further lowpass filter which passes the quadrupled frequency, down converted signal to a further amplifier. Finally, a direct approach spectrum analyzer analyzes the amplifier output signal which is an intermediate frequency signal in the most sensitive range of the spectrum analyzer for phase noise measurements on the device under test.

Phase noise measurements utilizing a frequency down conversion/multiplier, direct spectrum measurement technique

A test system for evaluating the operating state of a headend of a broadband communications network for communicating telephony signals between a telephony system and subscribers of communications services. Modulators at the headend transmit telephony signals in the forward band of the broadband communications network. The forward telephony channels are demodulated and demultiplexed by a plurality of subscriber terminals into individual telephony signals directed to an addressed subscriber. Signals returning from subscribers are digitized into standard telephony signals onto the reverse band of the broadband communications network, and demodulated by demodulators of the headend into a standard telephony signal that is interfaced to the telephony network. The test system evaluates the operating state of a selected demodulator of the headend by modulating a carrier with a predetermined data pattern to generate an upstream test signal. The upstream test signal is transmitted to the selected demodulator, which responds by outputting a detected upstream test signal. The test system compares the detected upstream test signal to the data pattern to generate error measurements that support an evaluation of the operating state of the selected demodulator. For an ingress test, the upstream signals present on the selected upstream channel are combined with the upstream test signal, and this signal combination is analyzed to determine the status of the selected upstream channel and the selected demodulator. The test system evaluates the operating state of a selected modulator of the headend in response to receiving a downstream test signal generated by the selected modulator. The test system outputs a detected downstream test signal in response to the downstream test signal. In turn, the test system conducts error measurements in response to the detected downstream test signal that support an evaluation of the operating state of the selected modulator.

Testing facility for a broadband communications system

A direct current and a modulation signal are simultaneously applied to contact pads on a device under test, such as a laser diode, with a probe that reduces signal distortion and power dissipation by transmitting a modulated signal through an impedance matching resistor and transmitting of a direct current over a second signal path that avoids the impedance matching resistor.

Probe for combined signals

A probe measurement system for measuring the electrical characteristics of integrated circuits or other microelectronic devices at high frequencies.

Probe for testing a device under test

A probe suitable for probing a semiconductor wafer that includes an active circuit. The probe may include a flexible interconnection between the active circuit and a support structure. The probe may impose a relatively low capacitance on the device under test.

Active wafer probe

Apparatus for measuring the phase noise content of a microwave signal source (10) includes a microwave cavity (22) resonant at a fixed frequency, signal generating means (23) operable to generate a frequency representing the difference between the source frequency and that of the resonant cavity, and mixing means (20) for combining the outputs of the source and the signal generating means. The output from the resonant cavity (22) is applied to a phase detector (15) together with a portion of the output of the mixing means (20) and the output of the phase detector (15) represents the phase noise content of the output of the microwave source (10). The signal generating means (23) includes a voltage-controlled oscillator the frequency of which is controlled by an output from the phase detector means (15) so as to maintain the output of the mixing means (20) at the resonant frequency of the microwave cavity (22).

Jeffrey Stoker

Papers

Microwave noise measuring apparatus