Low Voltage Reference Current Generator Circuit Design
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Solution Overview
Problem
Reference current generators fail to operate effectively at low supply voltage levels below 1.2 V, as the sum of the minimum operating voltages of the current sink and current mirror exceeds the available supply voltage, leading to operational failures in memory devices.
Innovation Solution
A reference current circuit design that includes an input leg with a current sink and a first resistor connected between the supply voltage node and the output of the current sink, and an output leg with a second resistor and a control transistor, where an operational amplifier ensures the voltage on the output leg matches the voltage on the input leg, maintaining the current sink's operating voltage above its minimum even at low supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional reference current generator architecture using a current sink and current mirror is used, then the circuit can generate reference current effectively at normal supply voltages, but the circuit fails to operate when supply voltage falls below the sum of minimum operating voltages of the current sink and current mirror (approximately 1.2 V or lower)
Solution Approach 1:
The reference current generator is divided into separate functional segments: a reference voltage generator that operates independently at ultra-low voltages, and a current mirror stage that receives this reference voltage. This segmentation allows each segment to be optimized for low-voltage operation, with the reference voltage generator producing a stable reference that enables the current mirror to function at supply voltages below 1.2 V
Solution Approach 2:
The invention changes the operating parameters by introducing a reference voltage node that operates at a different voltage level than the main supply. The reference voltage generator produces a stabilized reference voltage that is then used to control the current mirror, allowing the circuit to operate reliably at supply voltages as low as 0.8 V by decoupling the reference generation from the main supply voltage variations
2Adaptability or versatility
If resistors are used in the reference current generator to reduce voltage drops, then the voltage headroom is reduced enabling lower supply voltage operation, but the precision of current matching and voltage regulation becomes more difficult to maintain
Solution Approach 1:
An operational amplifier is introduced as an intermediary element to maintain precise voltage matching between the reference leg and output leg. The op-amp actively regulates the voltages across the resistors, ensuring that despite the reduced voltage headroom from using small resistance values, the current matching precision is maintained through active feedback control
Solution Approach 2:
The operational amplifier implements a feedback mechanism that continuously monitors and adjusts the voltages across the resistors in the reference and output legs. This feedback ensures that the voltage drops across the resistors remain equal, maintaining precise current matching even when operating with minimal voltage headroom at ultra-low supply voltages
Data Source
AI summary
A reference current circuit usable in a memory circuit has an input leg comprising a current sink and a first resistor connected between the current sink and a voltage supply node, and has an output leg connected between the supply voltage node and a load. The output leg includes a second resistor and a control transistor. The load is connected in current flow communication with the control transistor. An amplifier has a first input connected to the output node of the current sink in the input leg and a second input connected to the second resistor. An output of the amplifier is connected to the gate of the control transistor.