Oscillator Circuit with Capacitor Reinitialization for Stable Frequency
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Solution Overview
Problem
Conventional oscillator circuits in semiconductor integrated circuits exhibit a high dependence of oscillation frequency on the power supply voltage, which can fluctuate due to battery deterioration or other factors.
Innovation Solution
An oscillator circuit design that includes a reference current circuit, a capacitor, a charging and discharging circuit with a switching mechanism, and a detection circuit, where the charging and discharging operations alternate, with the discharging operation always starting from the power supply voltage, reducing the oscillation frequency's dependence on the power supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conventional oscillator circuit charges and discharges the capacitor continuously, then the oscillation frequency is generated, but the oscillation frequency becomes highly dependent on the power supply voltage
Solution Approach 1:
The invention applies preliminary action by initializing the capacitor voltage to the power supply voltage Vdd before each discharging operation begins. The switching circuit SW is controlled to set the capacitor C1 voltage to Vdd at the rising edge of the clock signal, ensuring that the discharging operation always starts from a known reference state. This preliminary initialization eliminates the dependency on previous charging states and stabilizes the oscillation frequency against power supply voltage variations.
2Reliability
If the capacitor voltage is not reinitialized to power supply voltage, then the circuit operation is simpler, but the oscillation frequency varies with power supply voltage changes
Solution Approach 1:
The invention implements periodic action by alternately switching between charging and discharging operations at each clock cycle. The switching circuit SW is controlled by the clock signal to periodically initialize the capacitor voltage to Vdd at the rising edge, then discharge through the reference current at the falling edge. This periodic reinitialization ensures consistent oscillation frequency while maintaining regular, predictable circuit operation that simplifies control logic.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design stabilizes the oscillation frequency by ensuring the discharging operation consistently begins from the power supply voltage, thereby minimizing its variation with changes in power supply voltage.
Implementation Method 1
a capacitor C, a Schmidt inverter STV detecting a voltage of a node N of the capacitor C
Implementation Method 2
a P-channel type MOS transistor M1 and an N-channel type MOS transistor M2 where an output of the Schmidt inverter STV is inputted to respective gates
Implementation Method 3
a Schmidt inverter STV detecting a voltage of a node N of the capacitor C, a P-channel type MOS transistor M3 serially connected with the P-channel type MOS transistor M1 and flowing a reference current I1
Data Source
AI summary
The invention provides an oscillator circuit that reduces the dependence of an oscillation frequency on a power supply voltage. A charging and discharging circuit is a circuit switchable between an initializing operation setting an initial voltage for discharge and a discharging operation, and outputs a clock when the discharge is completed. The clock is inputted to a set terminal of a RS flip-flop. A signal formed by delaying an output signal of the RS flip-flop by a delay circuit is inputted to a reset terminal of the RS flip-flop. The output signal of the RS flip-flop is inverted to a discharge enable signal by an inverter, and the discharge enable signal is inputted to a switching circuit of the charging and discharging circuit. With this structure, the charging and discharging circuit alternately repeats the initializing operation and the discharging operation, and by the initialization the discharging operation is always started from the power supply voltage.