Mixer Biasing Using Baseband Common-Mode Voltage Tracking
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Solution Overview
Problem
Mixer biasing techniques that rely on supply or ground voltages are prone to variations, leading to improper transistor biasing, increased harmonic distortion, and conversion loss in radio-frequency devices, which degrade communication performance.
Innovation Solution
Implementing a biasing system that uses baseband filter common-mode voltage as a reference to generate a bias voltage for mixer transistors, allowing the bias voltage to track changes in the baseband signal and remain independent of supply and ground voltage variations, and further tuning for operational and process variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If biasing is performed using supply or ground voltages, then the biasing circuit is simple to implement, but the bias voltage is prone to variations from temperature, supply voltage, and ground voltage changes, leading to improper transistor biasing and increased harmonic distortion
Solution Approach 1:
The patent introduces a baseband filter common-mode voltage as an intermediary reference for biasing the mixer transistor. This common-mode voltage serves as a mediator that is less susceptible to supply and ground voltage variations, thereby providing a more stable bias reference while maintaining circuit simplicity.
Solution Approach 2:
The biasing circuit uses the baseband filter common-mode voltage as a feedback reference to dynamically adjust the mixer transistor bias voltage. This feedback mechanism ensures that the bias voltage tracks changes in the baseband signal and compensates for variations in supply and ground voltages, improving bias stability.
2Reliability
If bias voltage is made independent of supply and ground voltages by using baseband filter common-mode voltage, then bias voltage stability improves, but the biasing circuit complexity increases
Solution Approach 1:
The baseband filter common-mode voltage node is utilized for multiple purposes: it serves as the reference for biasing the mixer transistor and also reflects the baseband signal characteristics. This multi-functionality approach allows the biasing circuit to achieve improved stability without proportionally increasing complexity, as an existing signal node is repurposed.
3Reliability
If proper biasing is maintained through tracking baseband signal voltage changes, then harmonic distortion and conversion loss are reduced, but the biasing circuit requires additional components and complexity
Solution Approach 1:
The biasing circuit is designed to automatically track and adjust itself based on the baseband filter common-mode voltage without requiring external control circuits or additional active components. The circuit self-adjusts the bias voltage in response to changes in the baseband signal, achieving improved performance while minimizing added complexity.
Data Source
AI summary
An apparatus is disclosed for mixer biasing with baseband filter common-mode voltage. In an example aspect, the apparatus includes a mixer, a baseband filter, and a bias circuit. The mixer has a mixer transistor that is coupled to a bias node and a baseband node. The baseband filter is coupled to the mixer via the baseband node. The baseband filter is configured to operate with a common-mode reference voltage that is associated with a common-mode voltage applied at the baseband node. The bias circuit is coupled to the baseband filter and the bias node. The bias circuit is configured to receive the common-mode reference voltage from the baseband filter and generate, at the bias node, a bias voltage for biasing the mixer transistor based on the common-mode reference voltage.