Dynamic-Bias Current Sink for Fast Floating-Rail Transients
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Solution Overview
Problem
Conventional current-sinking circuits in power management units (PMUs) or switching regulators (SRs) face challenges in efficiently sinking large transient currents while maintaining a stable floating-rail voltage, especially at battery voltages below 2.7V, and require high quiescent biasing currents, leading to reduced efficiency.
Innovation Solution
A low-power, fast-transient current-sink is implemented using a dynamically controlled latch system with a set-reset (S-R) latch, comparator, and dynamic biasing circuit, which includes a current sinking switch controlled by the latch system output to sink transient load currents effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional current-sinking circuits use high quiescent biasing currents to enable fast transient load current sinking, then the transient current sinking capability is improved, but the power consumption increases and efficiency decreases
Solution Approach 1:
The patent applies dynamic biasing to the current-sinking circuit, where the biasing current is dynamically adjusted based on the operating conditions. During transient events, the biasing current increases to enable fast current sinking, while during normal operation, the biasing current reduces to minimize power consumption. This dynamic adjustment resolves the contradiction between fast transient response and low power consumption.
Solution Approach 2:
The patent changes the biasing current parameter dynamically based on the state of the circuit. By monitoring the floating-rail voltage and adjusting the biasing current accordingly, the system achieves fast transient response when needed while maintaining low power consumption during steady-state operation, thus resolving the contradiction between speed and energy efficiency.
2Adaptability or versatility
If floating-rail architecture uses 1.8V Gox devices to operate at battery voltages below 2.7V, then the operating voltage range is extended, but the minimum operating voltage is limited
Solution Approach 1:
The patent changes the gate-to-source voltage parameter by introducing a negative voltage on the floating rail, effectively increasing the voltage headroom available to the 1.8V Gox devices. This allows the circuit to operate reliably at battery voltages below 2.7V, extending the operating voltage range while maintaining device reliability.
Solution Approach 2:
The patent introduces a floating rail voltage as an intermediary between the battery voltage and the device operating voltages. By dynamically controlling this intermediate voltage, the system can accommodate a wider range of battery voltages while ensuring that the 1.8V Gox devices always operate within their specified voltage ranges, thus resolving the contradiction between voltage range and reliability.
3Device complexity
If conventional current-sinking circuits use floating-rail voltage generation with diode-connected transistors, then the circuit structure is simplified, but the minimum VSSHV is limited by diode voltage and Vdsat
Solution Approach 1:
The patent changes the voltage parameters by applying negative voltage to the floating rail, which effectively increases the available voltage headroom. This allows the circuit to achieve lower minimum operating voltages without complicating the basic floating-rail structure, thus resolving the contradiction between structural simplicity and voltage limitation.
Data Source
AI summary
A current-sink and method of using the same is provided for sinking transient load currents of a load coupled to a floating-rail. In one embodiment, the current-sink includes a latch system operable to receive a transient load current signal from the load and set a latch to apply a voltage to a gate of a current sinking switch. The current sinking switch includes a first source/drain (S/D) coupled to the floating-rail, and a second S/D coupled to ground, and is operable to sink the transient load current to provide a stable floating-rail voltage (VSSHV) on the floating-rail. Generally, the latch system further includes a dynamically biased comparator for comparing VSSHV to a reference voltage and resetting the latch when a difference is less than a predetermined voltage. A dynamic bias circuit coupled to a latch output enables the comparator only while the transient load current is present.