PLL Charge Pump Delay Control for Variable VCO Gain Transients
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Solution Overview
Problem
Phase lock loop (PLL) circuits with variable oscillator gain face increased transient responses and lock times due to transition discontinuities caused by using different charge pumps, which existing methods fail to adequately address.
Innovation Solution
A system and method that adjusts the current/output from the charge pump based on oscillator gain by introducing a programmable delay in the adapt mode of operation, adding a trickle current after a predetermined time period to minimize transient responses and reduce lock time across varying oscillator gains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If two different charge pumps (regular speed and faster speed) are used to reduce lock time, then signal acquisition speed is improved, but transition discontinuity increases causing increased transient response
Solution Approach 1:
A delay element is introduced as an intermediary component between the charge pump output and the VCO input. This delay element mediates the transition between different charge pump speeds by smoothing the current changes, thereby reducing transition discontinuity while maintaining the speed benefits of using multiple charge pumps
Solution Approach 2:
The system performs preliminary action by pre-charging or pre-discharging the delay element capacitor before switching between different charge pump speeds. This preliminary action prepares the circuit state to minimize abrupt transitions and reduce transient responses when switching between regular speed and faster speed charge pumps
2Object-generated harmful factors
If existing transient response reduction techniques are applied, then transient response is reduced for constant VCO gain, but the technique fails when VCO gain varies through the band of operation
Solution Approach 1:
The delay element's time constant is made dynamic by allowing it to be adjusted based on the VCO gain value. This enables the system to adapt the delay characteristics to match different VCO gain conditions, maintaining effective transient response reduction across the entire frequency tuning range rather than being fixed for a single gain value
Solution Approach 2:
The system changes the delay parameter (time constant) according to the VCO gain parameter. By dynamically adjusting the delay element's characteristics based on the operating point, the system maintains optimal transient response performance across variable VCO gain conditions
Data Source
AI summary
A system and method for reducing the transient responses in a phase lock loop (PLL) (100) with variable oscillator gain is disclosed. The system includes a charge pump (104) having an adapt mode and a normal mode of operation. The charge pump (104) also includes controlled trickle currents from current sources (208), (210) which are applied to the output (105), (107) of charge pump (104) to minimize the transient responses of the PLL (100). A programmable delay is provided in the charge pump (104) and is configured using a controller (122) based on the variable oscillator gain for the PLL (100). The configured programmable delay is used in the adapt mode of operation for adding a trickle current from the current source (210) to the adapt mode output (107).