Differential Amplifier Bias Circuit for Stable Current at Varying Common Mode
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Differential amplifier circuits face challenges in maintaining a constant output current over a wide range of common mode input voltages, leading to variability in output current, reduced timing margin, degraded slew rate, increased power consumption, and susceptibility to noise.
Innovation Solution
A bias circuit with current sources and a control circuit that generate pbias and nbias signals to maintain a constant current through a load circuit, adjusting based on reference signals to ensure consistent output current across the common mode input range by selectively controlling the conductivity of transistors in the current sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If n-channel and p-channel stages are both activated to improve amplifier performance, then output current increases, but output current variability increases and timing margin reduces
Solution Approach 1:
The bias circuit dynamically adjusts the tail current based on the common mode input voltage level. When both n-channel and p-channel stages are active, the bias circuit increases the tail current to compensate for the doubled output current, thereby maintaining constant output current and preserving timing margin across the entire common mode input range.
2Power
If n-channel and p-channel stages are both activated to improve amplifier performance, then output current increases, but power consumption increases
Solution Approach 1:
The bias circuit dynamically adjusts the tail current based on the common mode input voltage level. When both n-channel and p-channel stages are active, the bias circuit increases the tail current to compensate for the doubled output current, thereby maintaining constant output current and preserving timing margin across the entire common mode input range.
3Power
If n-channel and p-channel stages are both activated to improve amplifier performance, then output current increases, but noise susceptibility increases
Solution Approach 1:
The bias circuit dynamically adjusts the tail current based on the common mode input voltage level. When both n-channel and p-channel stages are active, the bias circuit increases the tail current to compensate for the doubled output current, thereby maintaining constant output current and preserving timing margin across the entire common mode input range.
4Stability of the object's composition
If selective activation of n-channel or p-channel stages is used to maintain constant current, then output current is constant at extreme ranges, but current variability occurs in the middle range where both stages operate
Solution Approach 1:
The bias circuit dynamically adjusts the tail current based on the common mode input voltage level. When both n-channel and p-channel stages are active, the bias circuit increases the tail current to compensate for the doubled output current, thereby maintaining constant output current and preserving timing margin across the entire common mode input range.
Solution Approach 2:
The bias circuit uses feedback from the common mode input voltage to automatically adjust the tail current. The control circuit monitors the operating region and modifies the bias current accordingly, creating a self-regulating system that maintains constant output current across all input conditions.
Data Source
AI summary
Bias circuits, amplifiers and methods are provided, such as those for providing bias signals over a range of common mode inputs for an amplifier to output a constant current. One example of a bias circuit is configured to generate a bias signal having a voltage magnitude according to a reference signal. The reference signal is indicative of a common mode input level of an input signal of the amplifier circuit and the bias circuit is further configured to adjust the bias signal over a range of common mode input levels. An amplifier receiving the bias signal is configured to generate an output signal in response to an input signal and drive an output current based on the voltage magnitude of the bias signal provided by the bias circuit.