Constant Voltage Output Buffer Circuit for High Speed Differential Signals
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Solution Overview
Problem
Existing output buffer circuits face limitations in operating speed due to high impedance caused by current sources, and struggle to independently regulate amplitude and common mode voltage in differential signals, leading to restricted amplitude ranges and fluctuations in common mode voltage.
Innovation Solution
A constant voltage type output buffer circuit is designed with a differential output buffer, replica circuit, current control circuit, and voltage control circuit, featuring switches, resistive elements, and operational amplifiers to control current and voltage, allowing independent regulation of amplitude and common mode voltage, and enhancing operating speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current source is used in the output buffer circuit, then the impedance is high and current control is precise, but the slew rate of the differential signal is limited and operating speed is lower
Solution Approach 1:
The patent divides the output buffer circuit into two independent control paths: one for amplitude control (via current source) and one for common mode voltage control (via voltage source). This segmentation allows each path to optimize its function without compromising the other, enabling high operating speed while maintaining precise current control.
Solution Approach 2:
The patent transitions from a single-dimension constant current control to a two-dimension control system that independently manages both amplitude (current-related) and common mode voltage. This dimensional expansion allows simultaneous optimization of both speed and control precision.
2Adaptability or versatility
If the resistance value of the combined resistor is reduced to increase operating band, then the operating band is improved, but the consumption current is doubled
Solution Approach 1:
The patent changes the control parameter from direct resistance adjustment to independent voltage and current control. By controlling the voltage source and current source separately, the circuit achieves wide operating band without the need to reduce resistance values that would double the consumption current.
3Device complexity
If source followers are used as voltage sources in the output buffer circuit, then the circuit structure is simple, but the amplitude and common mode voltage cannot be controlled and the amplitude is limited by threshold voltage
Solution Approach 1:
The patent replaces static source follower voltage sources with dynamic controllable voltage sources that can actively adjust their output. This allows the circuit to adaptively control both amplitude and common mode voltage according to operating conditions, overcoming the limitations of fixed threshold voltage in source followers.
4Ease of operation
If one voltage source is eliminated to enable amplitude control, then the amplitude control is achieved, but the common mode voltage has amplitude dependency and gets out of receivable range when amplitude is increased
Solution Approach 1:
The patent segments the control functions by maintaining both voltage source and current source with independent control loops. The voltage source specifically controls common mode voltage while the current source controls amplitude, eliminating the amplitude dependency problem in common mode voltage that occurs when voltage sources are eliminated.
5Ease of operation
If separate operational amplifiers are used for amplitude regulation and common mode voltage regulation, then both parameters can be controlled, but the two feedback controls influence each other and stable operation cannot be performed
Solution Approach 1:
The patent uses the current source as an intermediary element that decouples the two feedback controls. By having the current source respond to amplitude errors and the voltage source respond to common mode voltage errors independently, the system avoids the instability caused by相互 influencing feedback loops while maintaining independent control of both parameters.
Data Source
AI summary
A differential output buffer includes first and third switches and second and fourth switches which are connected in series respectively between a first voltage source and a current source, and a replica circuit includes a second voltage source which is equivalent to a first voltage source. A current control circuit controls a current flowing to the current source in such a manner that a voltage of a third node between two resistive elements connected in series between a first node between the first and third switches and a second node between the second and fourth switches and having an equal resistance value is equal to a reference voltage, for example, and a voltage control circuit generates a control signal in such a manner that a voltage of any node excluding an output terminal of the second voltage source in the current path is equal to a second reference voltage.