Correlators
Overview
A correlator is passive linear SAW tapped delay line with impulse response being a sequence of RF pulses (taps) of arbitrary amplitude and phase. The pulses are all at the Center Frequency (F0) and their repetition rate is called the Chip Rate (B). The number of pulses is called the Code Length (N). Most commonly, the tap amplitudes are equal and the tap phases are a pseudo-random sequence of 0 and 180 degrees. A Correlator is a matched filter to an input signal which is the time inverse of its impulse response. In this case the Correlator output is a spike of width 1/B with sidelobes <-10*log10(N) dB extending +-N/B on each side of the spike. The peak signal to noise ratio is improved by the Processing Gain 10*log10(N) dB. A Perfect sequence has all sidelobes –20*log10(N) dB. The longest Perfect sequence is the Barker Code with N=13.
Correlator Performance
| Practical Maximum Values | |
| Chip Rate B MHz | 100 |
| Length N | 500 |
| Length T=N/B us | 20 |
| Center Frequency MHz | 500 |
Key to Abbreviations
Material Code
STQ = 42.75 degree rotated Y cut, X propagating, SiO2, Temp Coeff = 3E-8
##YX-Q = 32 to 43 degree rotated Y cut, X propagating, SiO2, Temp Coeff = 3E-8
YZ-LN = Y cut, X propagating, LiNbO3, Temp Coeff = 94E-6
128YX-LN = 128 degree rotated Y cut, X propagating, LiNbO3, Temp Coeff = 75E-6
X112Y-LT = X cut, 112 degree from Y propagating, LiTaO3, Temp Coeff = 18E-6
Matching Code
external matching elements listed from source to load
series elements upper case, shunt elements lower case
R=resistor, L=inductor, C=capacitor, T=transformer, B=balun, S=saw
Z = internal impedance match
C = connectorized
O = ovenized
A = amplified
S = switched
M = multiplexed
W = weighted amplitude
# = used in module p/n #, or uses component p/n #, with hyperlink to that p/n
Notes:
- A Component is a hermetic SAW product with no DC connections
- A Module contains one or more Components
- A Subsystem contains multiple Modules
- Spurious is in the time domain. The principle spurious are feedthru and triple transit. ‘NA’ is designated in this column for Resonators in the Bandpass Filters section.
- ITAR unrestricted parts in standard packages, indicated by asterisks to the right of the Model numbers below, are available for web sale in small quantities.
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