Startup Bias Circuit for Stable Fully Differential Op-Amp Initialization
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Solution Overview
Problem
The common-mode feedback circuit in traditional receivers consumes excessive power and fails to stabilize the static operating point of fully-differential operational amplifiers during startup, leading to poor operating stability.
Innovation Solution
A startup circuit device is introduced, comprising resistors, transistors, and a comparator, which adjusts the input voltage to a target voltage, ensuring the fully-differential operational amplifier operates stably by connecting the first startup input terminal to the first amplification input terminal and the second startup input terminal to the second amplification input terminal, thereby improving stability during startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a common-mode feedback circuit is used to stabilize the static operating point of the fully-differential operational amplifier, then the operating stability is improved, but the power consumption increases significantly
Solution Approach 1:
The circuit is divided into two independent parts: a traditional common-mode feedback circuit for normal operation and a separate startup circuit for initialization. The startup circuit includes a startup capacitor connected between the output and inverting input, along with associated resistors and transistors, while the common-mode feedback circuit remains intact for stabilization during normal operation. This segmentation allows the startup function to be isolated, enabling power savings by disabling it after initialization while maintaining operating stability through the feedback circuit.
Solution Approach 2:
The startup circuit performs preliminary action by initializing the static operating point of the fully-differential operational amplifier before normal operation begins. The startup capacitor charges through resistors to establish the correct voltage levels at the inputs and output of the amplifier during power-up, ensuring the amplifier is properly biased before the main signal processing begins. This preliminary initialization prevents the amplifier from operating in an undefined state.
2Reliability
If the common-mode feedback circuit is used during startup, then the static operating point stabilization is improved, but the power consumption remains high during the startup phase
Solution Approach 1:
The startup circuit operates periodically rather than continuously. It is activated only during the startup phase through a control signal that enables the startup transistor. Once the startup capacitor is charged and the operational amplifier reaches its static operating point, the control signal disables the startup circuit. This periodic operation provides necessary stabilization during startup while avoiding continuous power consumption.
Solution Approach 2:
The startup circuit is temporarily used during startup and then discarded (disabled) once its function is completed. The startup capacitor retains the charged voltage to maintain the static operating point, allowing the startup circuit to be powered down. This approach recovers power by eliminating the startup circuit's power consumption after initialization, while the charged capacitor continues to provide the necessary bias conditions.
3Device complexity
If the fully-differential operational amplifier operates without proper startup initialization, then the device complexity is reduced, but the operating stability deteriorates
Solution Approach 1:
The startup circuit is nested within the existing filter circuit structure. The startup capacitor is connected in parallel with the feedback path of the fully-differential operational amplifier, and the startup transistor is integrated into the existing circuit nodes. This nesting allows the startup function to be added without requiring a completely separate circuit block, thereby limiting the increase in device complexity while still providing the necessary initialization for operating stability.
Data Source
AI summary
The present disclosure discloses a startup circuit device, a filter and a receiver. The startup circuit device is applicable to the filter that includes a fully-differential operational amplifier and a common-mode feedback circuit device connected in sequence. Both the first startup input terminal and the first startup output terminal are connected to a first amplification input terminal of the fully-differential operational amplifier, and both the second startup input terminal and the second startup output terminal are connected to a second amplification input terminal of the fully-differential operational amplifier. The startup circuit device is configured to adjust a received input voltage to a target voltage during startup of the fully-differential operational amplifier, and output the target voltage to the fully-differential operational amplifier, such that the fully-differential operational amplifier operates at the target voltage, and stability of the fully-differential operational amplifier during the startup can be improved effectively.