Digital RF Amplitude Modulator with Switched Amplifier Stages
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Solution Overview
Problem
Existing digital amplitude modulators for RF signals face inefficiencies in amplifying amplitude-modulated signals, particularly at modern wireless network frequencies, and struggle to control average power across a wide range in code-multiplexed transmissions like CDMA and WCDMA standards.
Innovation Solution
A digital amplitude modulator with a first and second variable gain amplifier, along with selectively activatable amplifier stages and a power controller unit, allows for independent control of amplitude modulation and power adjustment through digital gain control signals, enabling efficient power management and high power range capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If linear power amplifiers are used to amplify amplitude modulated signals, then the amplification accuracy is improved, but the energy efficiency deteriorates
Solution Approach 1:
The power amplifier is divided into multiple parallel elementary amplifiers (first group with full gain, second group with fractional gains). Each amplifier operates independently and can be selectively activated based on the required output amplitude, allowing efficient amplification of amplitude modulated signals without requiring linear operation across the entire power range.
Solution Approach 2:
The system dynamically selects and activates specific elementary amplifiers based on the instantaneous amplitude requirements of the modulated signal. The activation state of each amplifier is controlled dynamically to match the signal envelope, enabling high efficiency while maintaining amplification accuracy for amplitude modulated waves.
2Measurement precision
If additional elementary amplifiers with fractional gains are added to increase amplitude modulation resolution, then the amplitude modulation precision is improved, but the device complexity increases
Solution Approach 1:
Different elementary amplifiers are assigned different gain values (full gain and fractional gains like 1/2, 1/4, 1/8) to create a hierarchical structure. This allows the system to achieve fine amplitude resolution by combining a small number of amplifiers with different characteristics rather than using many identical amplifiers, thereby reducing overall device complexity.
Solution Approach 2:
The elementary amplifiers are designed with asymmetric gain values rather than uniform gains. This asymmetric configuration enables the system to achieve high amplitude resolution through logarithmic-like scaling, where each additional amplifier provides progressively finer control over the output amplitude, reducing the total number of components needed.
3Ease of manufacture
If input transformers are eliminated to reduce manufacturing costs and volume, then the manufacturing cost is improved, but the signal transmission reliability may deteriorate
Solution Approach 1:
The mechanical transformer coupling is replaced with direct electronic coupling through driving circuits. The driving circuits provide galvanic isolation and signal coupling without requiring magnetic transformers, eliminating the need for bulky and expensive transformer components while maintaining signal integrity through electronic means.
4Speed
If the number of windings in the output transformer is increased to operate at modern wireless frequencies, then the operating frequency range is improved, but the device complexity and volume increase
Solution Approach 1:
The output transformer is completely removed from the system architecture. Instead of using a transformer to couple the amplifiers to the load, the invention employs direct switching of the elementary amplifiers with appropriate impedance matching networks, eliminating the complexity and volume associated with high-winding-count transformers while enabling operation at modern wireless frequencies (0.7-5.8 GHz).
Data Source
AI summary
A digital amplitude modulator. The digital amplitude modulator is configured to modulate the amplitude of an input carrier signal based on input digital data and generate a corresponding output signal. The digital amplitude modulator includes a first variable gain amplifier for receiving the input carrier signal and generating a corresponding first amplified carrier signal, a second variable gain amplifier for receiving the input digital data and generating corresponding digital amplitude control data and a plurality of selectively activatable amplifier stages. Each amplifier stage receives a replica of the first amplified carrier signal and generates a corresponding second amplified carrier signal when activated. The output signal corresponds to a combination of the second amplified carrier signals generated by the activated amplifier stages.