Research On Multi Tau Correlator

Photon correlation technology, based on photon statistics, is an interdisciplinary science. As the main method for nano particle size distribution testing, photon correlation technology has attracted wide spread attention. Photon correlator, which carries out real time correlation operations, is the key equipment of photon correlation instruments. The performance of correlator determines the precision of photon correlation measurements. Up to now there are still no available domestic photon correlator products while the market demanding keeps increasing. Under such circumstance, the promotion of technology research and commercial industrialization of photon correlator product with independent intellectual property has become urgent which will brings huge economy and social benefits.Based on the preliminary work of the research group, the subjects of this paper expand around the extending of the correlater dynamic range and improving of the precision. The main work of this paper consists of:1. The linear, exponential and multi tau correlator structure was studied, and the conflict encountered in linear correlator between dynamic range and resolution was analyzed.2. A new reduced symmetric normalization method was presented in which a single monitor channel is shared by all the channels with the same sample time. Statistical accuracy of standard, symmetric and the proposed reduced symmetric normalization methods was analyzed. Both theory and measurements results showed that the new reduced normalization method can effectively offset the increasing evaluation bias in the utilization of multi tau correlator with apparently less hardware resource addition.3. In order to reduce the hardware costs and decrease the inferior limit of sample time, the clip correlation technology was studied. The calculation speed and accuracy of both clip correlator and full correlator were compared in practical measurements.4. A correlator dynamic ranges adaptive adjust method was presented in this paper. Through the selection of original sample time and redistributeon of correlator channel sample times, photon correlater dynamic range can be adaptively adjusted to match the decay range of autocorrelation function in measurements of random particle systems.5. Based on FPGA technology, a 256 channel multi tau clip correlater and a 256 channel multi tau full correlater were implemented respectively. The inferior sample time was about 28ns for the clip correlator and 36ns for the full correlator.In recent years, the main correlater producers have launched series of high pormance correlater products. To accelerate domestic manufacturing of correlator, lower the price in the native market has become an emergency problem. The work in this paper would contribute for this procedure.