RF Modulator Current-Mirror Predistortion for High Linearity
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Solution Overview
Problem
Existing RF modulators face challenges in achieving high linearity without the complexity and high current consumption associated with using an 8-phase mixer, leading to significant intermodulation distortion.
Innovation Solution
A novel RF modulator design utilizing a current mirror architecture with identical baseband and RF transistors, employing a current mirror principle to provide analog pre-distortion, even with a simple passive mixer, ensuring high linearity and reduced complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an 8-phase mixer is used to reduce RF harmonics and improve linearity, then linearity is improved, but device complexity increases
Solution Approach 1:
The invention divides the linearity improvement function into two separate stages: baseband predistortion and RF correction. The baseband stage applies initial predistortion to counteract expected nonlinearities, while the RF stage provides additional correction. This segmentation allows each stage to be simpler than an 8-phase mixer while achieving comparable overall linearity.
Solution Approach 2:
The baseband transistor applies predistortion to the input signal before it reaches the mixer stage. By pre-compensating for expected nonlinearities in the baseband stage, the subsequent RF stage requires less complex circuitry to achieve the desired linearity performance, avoiding the need for an 8-phase mixer.
2Object-generated harmful factors
If an 8-phase mixer is used to reduce intermodulation distortion, then intermodulation distortion is reduced, but current consumption increases
Solution Approach 1:
The current consumption for distortion reduction is segmented across two simpler stages rather than concentrated in one complex 8-phase mixer. The baseband transistor and RF transistor each consume less current individually, and their combined effect achieves the same intermodulation distortion reduction with lower total current consumption.
Solution Approach 2:
The invention uses simpler, lower-cost transistor implementations in the baseband and RF stages rather than expensive complex mixer circuitry. These simpler transistors consume less current while achieving the same distortion reduction through the predistortion approach.
3Device complexity
If a simple passive mixer is used to reduce complexity, then device complexity is reduced, but linearity deteriorates
Solution Approach 1:
The baseband transistor applies predistortion to the signal before it enters the simple passive mixer. This preliminary correction compensates for the linearity deficiencies that would otherwise require a complex 8-phase mixer, allowing the use of a simple passive mixer without sacrificing overall system linearity.
Solution Approach 2:
The baseband stage applies anti-distortion predistortion to counteract the expected nonlinearities introduced by the simple passive mixer. This preliminary counter-action ensures that the combined system achieves high linearity even though the mixer itself is simple and would normally produce distortion.
4Adaptability or versatility
If baseband and RF transistors have different gains, then design flexibility is improved, but linearity deteriorates
Solution Approach 1:
The invention changes the gain parameter relationship between baseband and RF transistors from being necessarily equal to being deliberately different. By designing the RF transistor with higher gain than the baseband transistor, the system achieves both design flexibility and maintained linearity through the predistortion mechanism that compensates for gain differences.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves high linearity with low current consumption and reduced complexity, suitable for integrated circuits, supporting various radio protocols like LTE and Bluetooth, with improved intermodulation distortion and adjacent channel power ratio performance.
Implementation Method 1
a baseband transistor arranged to pass some or all of the input current between a first terminal and a second terminal of the baseband transistor; an electrical connection between the input line and a control terminal of the baseband transistor
Implementation Method 2
The RF modulator mixes the baseband signal with a periodic signal generated by a local oscillator (LO) at an RF carrier frequency. The mixing process is intentionally non-linear, so that it generates sum and difference components at radio frequencies
Implementation Method 3
comprises a radio-frequency transistor; is configured to apply the radio-frequency mixed signal to a control terminal of the radio-frequency transistor so as to cause the radio-frequency transistor to pass a radio-frequency output current between a first terminal and a second terminal of the radio-frequency transistor
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A radio-frequency modulator (1-3) apparatus comprises a baseband stage (1), a mixer stage (2) and a radio-frequency stage (3). The baseband stage (1) comprises: an input line for receiving an input current (10) representative of a baseband input signal, a baseband transistor (11, 12) that passes some or all of the input current (10) between a first and a second terminal thereof, an electrical connection (13) between the input line and a control terminal of the baseband transistor (11, 12), and an output line connected to said control terminal. The mixer stage (2) receives a signal (BB_Ip, BB_In) from the baseband stage (1) and mixes it with a radio-frequency local-oscillator signal to generate a radio-frequency mixed signal (V_RFp, V_RFn). The radio- frequency stage (3) receives the radio-frequency mixed signal (V_RFp, V_RFn), applies the radio-frequency mixed signal (V_RFp, V_RFn) to a control terminal of a radio- frequency transistor (30, 31) causing it to pass a radio-frequency output current (I_RFp, I_RFn) between a first and a second terminal thereof, and outputs the radio- frequency output current (I_RFp, I_RFn) as an output signal (RFout).