High precision RF vector analysis system based on synchronous sampling
AssigneeUniversite Du Quebec A Trois-Rivieres
InventorsTapan K. Bose, Raymond Courteau
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Abstract
The signals to be measured are transformed in the system to discrete time digital signals by synchronous sampling. These digital signals are then processed by a digital signal processor for vector detection and for computing digital feedback sent to the sampling gates. The analyzer has improved characteristics in the area of linearity, drift and test port signal injection because of its highly optimized architecture based on synchronous sampling with digital feedback. It possesses unique characteristics such as the ability to tune to a harmonic or a subharmonic of the excitation frequency and a good sensitivity in a high impedance environment.
Claims13
An RF/microwave amplitude and phase measurement system comprising:
- a sampling system comprising a plurality of sampling gates, each sampling gate having an RF input terminal, an output terminal and a control terminal;
- a sampling strobe synthesizer operating at a .function..sub.S having an output terminal connected to the control terminals of said sampling gates;
- a discrete time signal processor (DTSP) having a processing signal having a predetermined number of samples per cycle, a plurality of input terminals, respective ones of the output terminals of said sampling gates being connected to respective ones of the input terminals of said DTSP, said DTSP also including a like plurality of channels, each channel being associated with a respective input terminal of said DTSP, and a plurality of output terminals;
- a reference clock;
- wherein:
- signals to be measured are connected to a respective one of said input terminals of said sampling gates;
- the sampling gates and the sampling strobe synthesizer being used in a synchronous sampling mode for frequency conversion and domain conversion;
- the outputs of the sampling system comprise sequences of discrete time signal signal samples where each sample represents the value of the input voltage at the sampling instant, said discrete time signal having a number of samples per cycle T equal to an inverse of a function of the fractional part of the input frequency .function..sub.IN of the input signals divided by the sample frequency .function..sub.s ;
- said function being given by:
- ##EQU7## and otherwise being given by 1-frac ##EQU8## the "frac" operator defining the fractional part of its argument;
- the sampling strobe syntheiszer comprising frequency synthesis means connected to the output of the reference clock;
- said number of samples per cycle in said signals processed by said DTSP being equal to T;
- and
- the outputs of the DTSP comprising, for each channel, the real and imaginary part of the signal input on that channel.
A sampling gate circuit comprising an RF input, a polarization feedback input, a gate output, a four-diodes sampling bridge gate means whose input side is connected to said RF input, operational amplifier to maintain said output side at the same potential as a voltage applied at the feedback input, a positive input of said amplifier being connected to the polarization feedback input, a negative input of said amplifier being connected to said gate output by a feedback network comprising a capacitor in parallel with a resistor, with the output of said operational amplifier being connected to said gate output and producing a voltage pulse for every sample whose magnitude is proportional to the difference between the sampled RF input and the voltage present at the polarization feedback input.
Dependencies are inferred from the claim text.