Cross-Coupled Variable Gain Amplifiers for Constant Phase Response
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Variable gain amplifiers (VGAs) face challenges in maintaining a constant phase response across a wide range of gain values, especially at millimeter-wave frequencies, leading to phase errors and degraded performance in phased array systems, particularly in 5G wireless communication systems, due to limitations in transistor technologies and conventional design trade-offs.
Innovation Solution
The implementation of VGAs with cross-couple switching arrangements, which maintain all transistors in an ON state and adjust coupling to achieve either maximum or minimum gain by in-phase addition or subtraction of currents, ensuring a substantially constant capacitance across gain states, thereby reducing phase errors and enhancing linearity and bandwidth without significant trade-offs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional VGA designs are used to achieve variable gain, then gain control is provided, but phase response varies across gain values leading to phase errors
Solution Approach 1:
The patent implements dynamic switching of transistor coupling configurations (series vs. parallel) based on desired gain levels. Switches dynamically reconfigure the transistor arrangement to maintain constant phase response across different gain states, resolving the contradiction between gain adaptability and phase precision
Solution Approach 2:
The patent changes the coupling parameter (series or parallel) of transistor terminals to achieve different gain states while maintaining constant phase response. By adjusting the coupling configuration rather than simply switching transistors on/off, the system achieves variable gain without phase errors
2Adaptability or versatility
If transistors are switched off to reduce gain, then gain control is achieved, but capacitance varies leading to phase errors
Solution Approach 1:
The patent keeps all transistors in the ON state continuously, avoiding switching them off. Instead, it uses switching arrangements to change the coupling of transistor terminals between series and parallel configurations, maintaining continuous useful action while achieving gain control and constant capacitance
Solution Approach 2:
The patent dynamically reconfigures the coupling arrangement of transistor terminals using switches. The switching arrangement changes the effective capacitance seen by the signal path from a variable value to a constant equivalent value across different gain states, resolving the contradiction between gain adjustability and capacitance stability
3Measurement precision
If additional transistors are added to maintain constant phase response, then phase accuracy improves, but device complexity and area increase
Solution Approach 1:
The patent makes the existing transistors serve multiple functions: they provide both gain control and phase response stabilization. The same transistors that control gain also maintain constant phase response when properly coupled, eliminating the need for additional dedicated phase-compensation transistors
Solution Approach 2:
The patent merges the phase compensation function with the gain control function into a unified transistor coupling arrangement. By combining these functions rather than implementing them separately, the design achieves constant phase response without adding significant complexity or area
4Adaptability or versatility
If conventional switching arrangements are used, then gain control is provided, but phase errors occur due to varying capacitance
Solution Approach 1:
The patent introduces switching arrangements as intermediaries that mediate between the transistors and the signal path. These switches control the coupling configuration (series or parallel) to present a constant equivalent capacitance to the signal, eliminating phase errors while maintaining gain control
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
An example VGA includes a transistor arrangement having a plurality of transistors configured to realize one or more gain step circuits of the VGA, and a cross-couple switching arrangement having a plurality of switches configured to selectively change the coupling of the terminals of at least some of the transistors depending on whether a given gain step circuit is supposed to be in an ON state or in an OFF state. Using the cross-couple switching arrangement advantageously allows keeping all of the transistors ON at all times during operation and changing the coupling of some transistor terminals to either realize an in-phase addition of currents flowing through various transistors to apply the maximum gain or realize a subtraction of currents to apply the minimum gain. Such a VGA may be inherently wideband, enabling a highly linear, wideband operation without having to resort to significant trade-offs with other performance parameters.