Output Pre-Driver Bias Switching for Tunable Signal Delay
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Solution Overview
Problem
In advanced technology nodes, such as the 12 nm fin-type field effect transistor (FinFET) node and beyond, increasing channel lengths of field effect transistors (FETs) to generate different pre-driver signals is difficult due to process limitations, leading to costly area and power consumption issues with inverter chains and non-tunable delay in existing output drivers.
Innovation Solution
A pre-driver circuit with multiple signal generation stages and a local switching bias circuit, including a bias voltage node and on/off switches, that selectively turns on to supply bias voltage only when needed, allowing for sequential and slower transitioning of pre-driver signals, reducing noise and enabling tunable delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If FETs with different channel lengths are used to generate different pre-driver signals, then delay tuning capability is improved, but manufacturing precision deteriorates due to process limitations at advanced technology nodes
Solution Approach 1:
The patent changes the controlling parameter from physical channel length to electrical bias voltage. By applying different bias voltages to the FETs in the inverter chain, different delay characteristics are achieved without requiring different physical channel lengths, thus avoiding manufacturing precision issues at advanced technology nodes
Solution Approach 2:
The patent introduces dynamic bias voltage control to make the delay characteristics adjustable. The bias voltage can be dynamically changed to tune the delay, transforming a static physical parameter (channel length) into a dynamic electrical parameter (bias voltage) that can be adjusted without changing the physical structure
2Area of stationary object
If inverter chains with remote voltage generators are used to generate pre-driver signals, then area consumption is reduced, but power consumption increases
Solution Approach 1:
The patent extracts the voltage generation function from a remote voltage generator and places it locally at each inverter stage through bias voltage nodes. This eliminates the need for a separate remote voltage generator while providing local bias control, thereby reducing both area and power consumption
3Loss of time
If inverter chains are used to generate pre-driver signals, then delay is provided, but delay tunability is lost
Solution Approach 1:
The patent makes the delay parameter tunable by changing the bias voltage parameter. Different bias voltages applied to the FETs result in different delay values, allowing the delay to be adjusted according to process variation and other conditions without changing the physical structure of the inverter chain
Data Source
AI summary
A disclosed pre-driver includes multiple signal generation stages and a switching bias circuit with a first switch and a second switch. The first switch and primary inverters in each of the stages all receive the same input signal. When the input signal transitions, the first switch turns on the bias circuit to supply a bias voltage to each of the stages. However, the primary inverters do not concurrently turn on. Instead, due to the bias voltage and some additional circuitry within each stage, the primary inverters turn on in sequence and slowly, thereby ensuring that pre-driver signals generated and output by the different stages, respectively, transition in sequence and at a relatively slow rate. Once the last pre-driver signal transitions, the second switch turns off the switching bias circuit. Optionally, a selected one of multiple bias voltages could be used in order to tune delay and transition times.