Cross-Coupled Crystal Oscillator Start-Up With Pulsed Gate Drive
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Solution Overview
Problem
Crystal oscillator circuits in high-frequency applications, such as the mmW frequency band, face challenges with prolonged start-up times and increased power consumption, as well as issues with parasitic oscillations, which are not adequately addressed by existing solutions.
Innovation Solution
A crystal oscillator circuit with a differential pair of transistors configured in a cross-coupled mode, combined with a kick-start circuit that injects pulses during start-up to reduce start-up time and minimize parasitic oscillations, utilizing a complementary differential pair for current reuse and disconnecting load capacitance during start-up to reduce dynamic power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the crystal oscillator operates at higher frequency to meet mmW band requirements, then the oscillation frequency is improved, but the power consumption increases
Solution Approach 1:
The kick-start circuit applies preliminary action by injecting start-up pulses before the oscillator begins normal operation. These pulses pre-chARGE the tank circuit and initiate oscillation buildup, allowing the oscillator to reach steady state faster and reduce the duration of high power consumption during start-up period.
Solution Approach 2:
The kick-start circuit employs periodic pulsing action rather than continuous operation. The start-up pulses are applied periodically for a limited duration to build up oscillation, then discontinued once the oscillator reaches steady state, thereby reducing overall power consumption compared to continuous high-frequency operation.
2Loss of time
If the start-up time is reduced to meet fast transmission requirements, then the transmission speed is improved, but the power consumption during start-up increases
Solution Approach 1:
The kick-start circuit performs preliminary action by pre-charging the tank circuit with start-up pulses before normal oscillation begins. This preliminary energy injection reduces the time required for oscillation buildup while concentrating power consumption into a controlled, limited-duration pulse sequence rather than prolonged high-power operation.
Solution Approach 2:
The kick-start circuit implements skipping by rushing through the start-up period with intensive pulsed action. The start-up pulses quickly drive the oscillation amplitude from zero to steady state in minimal time, then the circuit transitions to normal low-power operation, effectively skipping the prolonged high-power start-up phase.
3Productivity
If the crystal oscillator is used in mmW band applications with shorter transmission units, then the data throughput is improved, but the start-up time becomes a limiting factor
Solution Approach 1:
The kick-start circuit applies preliminary action by pre-initiating oscillation with start-up pulses before data transmission begins. This ensures the oscillator is already at steady state when transmission starts, eliminating start-up time from the critical transmission path and maximizing data throughput for short transmission units.
Solution Approach 2:
The kick-start circuit enables continuity of useful action by ensuring the oscillator is ready immediately when transmission is needed. The start-up pulses continuously build oscillation amplitude during the start-up period, and once steady state is reached, the useful action of data transmission can proceed without interruption or delay.
Data Source
AI summary
A crystal oscillator circuit comprises a crystal; oscillator circuitry for generating a crystal oscillation signal at an oscillation frequency; and a kick-start circuit for injecting pulses into the crystal during a start-up period. The oscillator circuitry comprises a differential pair of transistors and can operate in an oscillating mode or a start-up mode. In the oscillating mode, the differential pair of transistors are cross-coupled so that a gate terminal of one transistor is coupled to a drain terminal of the other transistor, and vice versa, and the drain terminals are coupled to the crystal to generate the crystal oscillation signal. In the start-up mode, the kick-start circuit drives the gate terminals of the transistors with said pulses. This crystal oscillator circuit has a decreased start-up time compared to prior art solutions and a reduced influence of parasitic oscillations.