Reconfigurable OTA Filter for Mixer Impedance and Linearity
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Solution Overview
Problem
Existing operational transconductance amplifier (OTA) based filters in communication devices face challenges in maintaining linearity and minimizing gain loss across different frequency bands, particularly in mixer circuits with varying input impedances.
Innovation Solution
A reconfigurable filter circuit with a controller that selectively couples output circuits with different resistors based on operation frequency, using a combination of OTAs and switches to maintain constant gain and improve linearity, while minimizing gain loss by using small transistors for switches to avoid parasitic capacitance and stability issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single output circuit is used in the filter, then the device complexity is reduced, but the linearity and gain loss performance deteriorate across different frequency bands
Solution Approach 1:
The filter circuit dynamically reconfigures its output circuit based on the operating frequency band. A controller selectively enables either the first output circuit (with first resistor) or the second output circuit (with second resistor) depending on whether the mixer operates in the first or second frequency band, allowing the filter to adapt its characteristics to maintain optimal linearity performance across different bands
Solution Approach 2:
The invention changes the output resistance parameter of the filter by selecting different resistors (first resistor with higher resistance, second resistor with lower resistance) based on the operating frequency. This parameter adaptation allows the filter to compensate for the varying input impedance of the mixer across frequency bands, thereby maintaining consistent linearity and gain performance
2Reliability
If the filter uses output circuits with different resistors for different frequency bands, then the linearity is improved, but the device complexity increases
Solution Approach 1:
The filter incorporates dynamic reconfiguration capability through a controller that switches between different output circuits based on frequency band detection. This dynamic adaptation enables the filter to maintain optimal linearity performance across multiple frequency bands by selecting the appropriate output circuit (first or second) matched to the current operating conditions
Solution Approach 2:
The filter is designed with multi-functionality to operate effectively across different frequency bands by incorporating both first and second output circuits with different resistance values. The controller enables the filter to universally handle various operating conditions (first frequency band or second frequency band) by selecting the appropriate output circuit, making the filter adaptable to different mixer input impedance characteristics
3Ease of operation
If large transistors are used for switches in the filter, then the switching capability is improved, but parasitic capacitance increases causing stability issues
Solution Approach 1:
The invention optimizes the transistor size parameter for the switches used in the reconfiguration process. By carefully selecting small transistor sizes for the switches while maintaining adequate switching capability, the design minimizes parasitic capacitance that would otherwise degrade filter stability. This parameter optimization allows the switches to function effectively without introducing harmful parasitic effects
Data Source
AI summary
Aspects of the disclosure provide a circuit having a filter circuit and a controller. The filter circuit drives a load circuit having different input impedances under different operation conditions. The filter circuit is configured to have a first output circuit coupled with a first resistor and a second output circuit coupled with a second resistor. The controller is configured to generate control signals to select one of the first output circuit and the second output circuit based on an operation condition of the load circuit.