Floating-Ground Loop Filter Precharge for Faster PLL Lock
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Solution Overview
Problem
Conventional lock loop circuits, such as PLL circuits, take too long to lock frequency and phase, and they suffer from current leakage to ground, which increases power consumption and noise.
Innovation Solution
A lock loop circuit with a floating ground loop filter and a precharge circuit that bypasses capacitive elements upon enable, allowing for faster locking of frequency and phase, and reducing leakage current by using a synchronized feedback divider and bypass switch circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional loop filter circuit is used, then circuit stability is maintained, but lock time is too long
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitive elements in the loop filter before the PLL circuit begins normal operation. The precharge circuit charges the capacitors to an initial voltage level that corresponds to the expected steady-state operating point, so when the PLL is enabled, the loop filter is already prepared and does not need to charge from zero, significantly reducing lock time.
Solution Approach 2:
The patent segments the loop filter circuit into multiple capacitive elements (first capacitor and second capacitor) with different time constants. The first capacitor has a smaller time constant for faster charging, while the second capacitor has a larger time constant for stability. This segmentation allows the circuit to achieve both fast lock time and stable operation.
2Reliability
If capacitive elements are used in loop filter, then filtering performance is improved, but current leakage to ground increases
Solution Approach 1:
The precharge circuit charges the capacitive elements to their target voltage levels before normal operation begins. Once charged, the capacitors hold their voltage without requiring continuous current from the error detector, significantly reducing steady-state power consumption while maintaining filtering performance.
Solution Approach 2:
The patent implements periodic action through the precharge circuit that operates only during the initial lock period, then disconnects. The main loop operates periodically with the error detector providing current only when phase/frequency errors exist, rather than continuous current flow, reducing overall power consumption.
3Loss of time
If loop precharger is added, then lock time is reduced, but circuit complexity increases
Solution Approach 1:
The patent merges the precharge function with the existing loop filter circuit by integrating the precharge circuit directly into the loop filter structure. The precharge circuit shares common nodes and capacitive elements with the loop filter, so the precharge functionality is added without requiring completely separate circuit components, minimizing overall complexity increase.
4Reliability
If multiple capacitive elements are used, then filtering performance is improved, but current leakage increases
Solution Approach 1:
By pre-charging multiple capacitive elements to their steady-state voltage levels, the patent eliminates the need for continuous charging current that would generate noise. The capacitors remain at stable voltages without ripple or fluctuation, reducing noise generation while maintaining the filtering benefits of multiple capacitive elements with different time constants.
Data Source
AI summary
A lock loop circuit (230) includes a floating ground loop filter circuit (302) and a precharge circuit (304). The floating ground loop filter circuit includes at least one capacitive element (326, 328). The floating ground loop filter circuit provides a steering signal (334) for a controllable oscillator circuit (306) in response to a precharge signal (347). The precharge circuit provides the precharge signal in response to lock loop enable information (226). The precharge circuit controls the floating ground loop filter to bypass the at least one capacitive element for a period of time (606) in response to the lock loop enable information.