Radiation-hardened charge pump topology

A radiation-hardened phase-locked loop, comprising:

• a first charge pump that includes a first charge pump output;
• a second charge pump that includes a second charge pump output;
• a third charge pump that includes a third charge pump output;
• a first coincidence detector that receives as inputs the first charge pump output and the second charge pump output and produces as an output a first coincidence signal, wherein the first coincidence signal is at logic “high” if the first charge pump output and the second charge pump output are within a defined tolerance of one another, and wherein the first coincidence signal is at logic “low” if the first charge pump output and the second charge pump output are not within the defined tolerance of one another;
• a second coincidence detector that receives as inputs the second charge pump output and the third charge pump output and produces as an output a second coincidence signal, wherein the second coincidence signal is at logic “high” if the second charge pump output and the third charge pump output are within the defined tolerance of one another, and wherein the second coincidence signal is at logic “low” if the second charge pump output and the third charge pump output are not within the defined tolerance of one another;
• decision logic that receives as inputs the first coincidence signal and the second coincidence signal and produces as an output a select signal based on the first coincidence signal and the second coincidence signal, wherein the decision logic produces a logic “high” select signal if the first coincidence signal is logic “high” and the second coincidence signal is logic “low”, and wherein the decision logic produces a logic “low” select signal if the first coincidence signal is logic “low” or if both the first and second coincidence signals are logic “high”;
• an analog 2:1 multiplexor that selects the second charge pump output if the select signal is logic “high” and selects the first charge pump output if the select signal is logic “low”;
• a first voltage controlled oscillator that produces a first feedback clock signal;
• a second voltage controlled oscillator that produces a second feedback clock signal;
• a third voltage controlled oscillator that produces a third feedback clock signal;
• a first phase frequency detector that receives as inputs a reference clock signal and the first feedback clock signal and produces an output to the first charge pump;
• a second phase frequency detector that receives as inputs the reference clock signal and the second feedback clock signal and produces an output to the second charge pump;
• a third phase frequency detector that receives as inputs the reference clock signal and the third feedback clock signal and produces an output to the third charge pump;
• a first loop filter that filters the first charge pump output;
• a second loop filter that filters the second charge pump output;
• and
• a third loop filter that filters the third charge pump output.

A method for radiation-hardening a charge-pump circuit, comprising:

• comparing, using an analog comparator, a first analog charge pump signal from a first charge pump to a second analog charge pump signal from a second charge pump to determine whether the first analog charge pump signal and the second analog charge pump signal are in a defined coincidence band of one another, wherein comparing the first analog charge pump signal from the first charge pump to the second analog charge pump signal from the second charge pump includes comparing to determine whether a single event upset (SEU) has occurred at one or more of the first charge pump and the second charge pump;
• selecting either the first analog charge pump signal or the second analog charge pump signal based on the determination;
• outputting the selected charge pump signal;
• comparing the second analog charge pump signal to a third charge pump signal from a third charge pump;
• and
• applying logic to the first comparison and the second comparison to determine whether the first analog charge pump signal or the second analog charge pump signal is selected.