Self-Biased Zero-Temperature-Current Reference Startup Circuit
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Solution Overview
Problem
Conventional current reference circuits in modern integrated circuits face instability due to high positive feedback loop gain, leading to oscillations and requiring large compensation capacitors, which are inefficient in high-performance applications.
Innovation Solution
A current reference circuit with a continuous base current fed from the power supply through a diode-configured transistor, using a small Miller-connected capacitor to compensate loop gain and avoid positive feedback startup, ensuring stable startup and operation over a wide range of power supply voltages and temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional positive feedback startup circuits are used, then startup is achieved, but oscillations occur and large compensation capacitors are required
Solution Approach 1:
The patent extracts and removes the positive feedback startup circuit from the conventional design. Instead of using a separate startup circuit with high gain that causes oscillations, the invention uses a minimal continuous base current fed from the power supply through a diode-configured transistor, eliminating the need for large compensation capacitors while ensuring stable startup.
Solution Approach 2:
The patent introduces a diode-configured transistor as an intermediary element that provides a controlled base current to the bipolar transistor. This intermediary structure regulates the startup current flow, preventing the high gain conditions that lead to oscillations while still enabling reliable transistor activation during power-up.
2Reliability
If high positive feedback loop gain is used, then startup is achieved, but oscillations occur
Solution Approach 1:
The patent changes the key parameter of feedback gain from high (conventional) to low (invention). By using a diode-configured transistor with inherent current regulation properties instead of a high-gain amplifier, the loop gain is naturally limited to a low value that prevents oscillations while still providing sufficient startup drive current for reliable operation.
3Stability of the object's composition
If large compensation capacitors are used, then oscillations are suppressed, but circuit efficiency decreases
Solution Approach 1:
The patent removes the large compensation capacitor from the circuit design. By eliminating the positive feedback startup mechanism that requires such capacitors for stability, the invention achieves oscillation suppression through the inherent current-regulating properties of the diode-configured transistor, thereby improving circuit efficiency and reducing component count.
Data Source
AI summary
A current reference circuit is disclosed. A small startup current is defined as the base current into a bipolar transistor with its collector-emitter path connected in series with a resistor between the power supply voltage and ground. This startup current is conducted via a diode-connected MOS transistor in a first leg of a current mirror. Temperature compensation is maintained by a reference leg in the current mirror that includes a bipolar transistor having an emitter area N times larger than that of a bipolar transistor in a second leg of the current mirror, to establish a temperature-compensated current in the reference leg. A compensation capacitor connected between the collector and base of a bipolar transistor in the first leg suppresses oscillation, and can be modest in size due to the Miller effect.