Super Source Follower Amplifier With Adjustable Gain for MEMS
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Solution Overview
Problem
Conventional source follower amplifiers for MEMS capacitive transducers suffer from load-dependent gain and distortion, particularly for large output signals, and have fixed gain that cannot be adjusted to compensate for manufacturing variations or dynamic range requirements.
Innovation Solution
A super source follower amplifier circuit with a feedback impedance network that includes capacitors and resistors, allowing for adjustable gain and reduced output impedance, implemented as an integrated circuit with a Class A or Class AB configuration to provide a low noise pre-amplifier with programmable gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional source follower amplifier is used, then the circuit is simple and power consumption is low, but the gain is fixed at approximately unity and cannot be adjusted
Solution Approach 1:
The patent applies dynamics by making the amplifier gain adjustable through a control voltage that modifies the transconductance of the input transistor. The gain can be dynamically changed from approximately unity to significantly higher values, allowing the same circuit to adapt to different application requirements without redesign
Solution Approach 2:
The patent changes the electrical parameters of the amplifier by using a control voltage to modify the bias conditions and transconductance of the input transistor. This allows continuous adjustment of the gain parameter while maintaining the source follower topology, resolving the contradiction between fixed gain and adaptability
2Object-affected harmful factors
If bias current is increased to reduce output impedance, then output impedance is reduced, but power consumption increases
Solution Approach 1:
The patent applies feedback by using a portion of the output signal to control the bias current of the input transistor. This feedback mechanism dynamically adjusts the operating point to optimize the trade-off between output impedance and power consumption, allowing low output impedance to be achieved without proportionally increasing power consumption
Solution Approach 2:
The patent makes the bias current dynamic rather than fixed, allowing it to be adjusted based on operating conditions. This dynamic biasing enables the circuit to achieve low output impedance when needed while consuming less power during normal operation, resolving the contradiction between these two parameters
3Use of energy by moving object
If a simple source follower amplifier is used, then power consumption is low, but distortion increases for large output signals
Solution Approach 1:
The patent uses feedback to linearize the amplifier operation. By feeding back a portion of the output signal to control the input transistor bias, the circuit compensates for non-linear effects that cause distortion, allowing large output signals to be produced with minimal distortion while maintaining low power consumption
Solution Approach 2:
The patent applies preliminary action by pre-biasing the input transistor optimally using feedback from the output signal. This preliminary bias adjustment occurs continuously to prevent distortion before it occurs, rather than trying to correct distortion after it occurs, thereby maintaining low distortion at large signal levels without increasing power consumption
Data Source
AI summary
This application relates to amplifier circuitry for amplifying a signal from a MEMS transducer. A super source follower circuit (40) is provided which includes a feedback path from its output node (Nout) to a control bias node (BC) in order to provide a preamplifier signal gain that may be greater than unity. A first transistor (M1) is configured to have its gate node connected to an input node (NIN) for receiving the input signal (VIN) and its drain node connected to an input node (X) of an output stage (A). The source node of the first transistor is connected to the output node (NOUT). A current source (I2) is configured to deliver a current to the drain node of the first transistor (M1), wherein the current source (I2) is controlled by a bias control voltage (VBC) at the bias control node (BC). A feedback impedance network (Z1) comprising a first port connected to the output node (NOUT) and a second port connected to the bias control node (BC) is provided.