Single-Balanced Mixer Architecture With Dummy Load Noise Rejection
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Solution Overview
Problem
Existing mixer architectures, such as single-balanced and double-balanced mixers, face limitations in noise rejection and power consumption, with double-balanced mixers requiring fully differential LNAs that consume more power and occupy more area, while single-balanced mixers have poor noise rejection properties.
Innovation Solution
A mixer design that incorporates a single-ended LNA coupled with a single-balanced portion and a dummy portion, utilizing a dummy load to match the impedance and improve noise rejection, allowing for area savings without compromising noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a double-balanced mixer is used, then noise rejection properties are improved, but power consumption and die area increase due to requiring a fully differential LNA
Solution Approach 1:
The mixer is divided into two separate single-balanced mixers instead of using one double-balanced mixer. Each single-balanced mixer handles one phase of the differential signal, allowing the use of a single-ended LNA while achieving noise rejection comparable to a double-balanced mixer.
Solution Approach 2:
Two single-balanced mixers are combined in a differential configuration to achieve the noise rejection performance of a double-balanced mixer. The outputs of both mixers are combined to produce the final differential output signal.
2Reliability
If a double-balanced mixer is used, then noise rejection properties are improved, but die area increases due to requiring a fully differential LNA
Solution Approach 1:
The mixer is divided into two separate single-balanced mixers instead of using one double-balanced mixer. Each single-balanced mixer handles one phase of the differential signal, allowing the use of a single-ended LNA while achieving noise rejection comparable to a double-balanced mixer.
Solution Approach 2:
A dummy load is introduced as a copy of the actual load to create a balanced input environment for the single-ended LNA. This dummy load mirrors the electrical characteristics of the real load, enabling proper differential operation without requiring a fully differential LNA.
3Reliability
If a balun is added to transform single-ended LNA output to fully differential signal, then noise rejection is improved, but die area increases and insertion loss occurs
Solution Approach 1:
The balun component is removed from the signal path entirely. Instead of adding a balun to transform single-ended to differential signals, the circuit is designed to natively support single-ended operation with a dummy load, eliminating the need for the balun and its associated die area and insertion loss.
Solution Approach 2:
The dummy load serves as an intermediary element that creates a balanced input environment without requiring active transformation components like baluns. It provides the necessary electrical balance through passive impedance matching.
4Area of stationary object
If a single-balanced mixer is used, then area is reduced, but noise rejection properties deteriorate
Solution Approach 1:
Two single-balanced mixers are combined in a differential configuration to achieve the noise rejection performance of a double-balanced mixer. The outputs of both mixers are combined to produce the final differential output signal.
Solution Approach 2:
The mixer is divided into two separate single-balanced mixers instead of using one double-balanced mixer. Each single-balanced mixer handles one phase of the differential signal, allowing the use of a single-ended LNA while achieving noise rejection comparable to a double-balanced mixer.
Data Source
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Figure 2A
Figure 2B
AI summary
Techniques for designing a single-balanced mixer coupled to a dummy portion with a dummy load to improve noise rejection. In an aspect, a single-ended signal (RF) from a stage preceding the mixer, e.g., a low-noise amplifier (LNA), is coupled to the input of the single-balanced mixer to be mixed with a local oscillator (LO) signal. A dummy portion replicating the topology of the single-balanced mixer is coupled to the single-balanced mixer to improve noise rejection, with the LO signal also provided to the dummy portion. The input of the dummy portion may be coupled, e.g., to a dummy load, which is designed to replicate the loading characteristics of the preceding stage, e.g., the LNA.