Signal selection and fault detection apparatus and method

A signal selector apparatus for selecting one of at least two input information signals, the signals possibly having errors resulting from null offsets, rate induced differences and gain differences and noise, the apparatus comprising:

• a signal selector module that receives and selects one of the at least two input signals as a selected information signal;
• a rate calculating module coupled to receive the selected information signal and having a first limiter that receives and limits the selected information signal by a selected threshold amount to produce a rate generated tolerance component signal that represents a worst case rate induced tracking error of the input signals;
• a gain error calculating module coupled to receive the selected information signal and having a first multiplier and a first subtractor, the first multiplier receiving the selected information signal and multiplying the selected information signal by a worst case gain tolerance constant to produce a gain tolerance component signal, and the first subtractor being coupled to the first multiplier and decreasing the gain tolerance component signal by a variable limit equalization rate to produce a gain generated tolerance component signal that represents a worst case gain induced offset of the input signals;
• a first adder coupled to the rate calculating module and the gain error calculating module that adds the rate generated tolerance component signal and the gain generated tolerance component signal to produce a total tolerance component signal;
• a retention filter coupled to the first adder that receives the total tolerance component signal and produces a delayed decay rate signal;
• a first maximum select module coupled to the first adder and the retention filter, the first maximum select module receiving the total tolerance component signal and the delayed decay rate signal and outputting as a dynamic threshold component signal, wherein the dynamic component threshold signal is the greater of the total tolerance component and delayed decay rate signals;
• a second adder coupled to the first maximum select module that adds a first constant value to the dynamic threshold component signal to produce a total threshold component signal;
• a first comparator coupled to the second adder that outputs a zero value as an output signal if the total threshold component signal is greater than an absolute value of a dynamic tracking error of the selected information signal, outputs a decrement value as the output signal if the absolute value of the dynamic tracking error is less than the first constant value, and outputs the absolute value of the dynamic tracking error as the output signal if the absolute value of the error is greater than the total threshold component signal;
• an integrator coupled to the comparator that integrates the output signal to produce an out-of-threshold integration signal;
• and
• a fault latching module coupled to the integrator and the signal selector module, the fault latching module receiving the out-of-threshold integration signal and latching the selected signal if the out-of-threshold integration signal exceeds a selected maximum value so that the signal selector module is prevented from selecting a latched signal.