Push-Pull Amplifier Calibration for Low Second-Order Distortion
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Solution Overview
Problem
Existing push-pull amplifiers in integrated circuits face challenges in minimizing second-order distortion due to production tolerances, which affect their linearity and performance, especially in direct conversion receivers where even order nonlinearity is a significant concern.
Innovation Solution
An electronic integrated circuit with a detection circuit having a push-pull amplifier with an adjustable size ratio between its transistor devices, allowing for calibration by applying a test signal and determining the optimal size ratio that minimizes second-order distortion, which is then applied to the main amplifier circuit to achieve low distortion levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If push-pull amplifier uses complementary transistor devices formed in different process steps, then even order non-linearity is reduced, but production tolerances cause mismatch and second order distortion increases
Solution Approach 1:
The patent applies preliminary action by measuring the second order distortion of each individual amplifier during production and storing the measured values in a lookup table. This pre-measurement and pre-correction approach allows the system to compensate for manufacturing variations without requiring complex real-time adjustments during operation.
Solution Approach 2:
The patent changes the parameter of transistor device sizing ratios based on the measured distortion characteristics. By adjusting the size ratio of transistor devices in the push-pull amplifier according to the stored measurement data, the system optimizes linearity performance while accounting for process variations.
2Device complexity
If antenna filter is removed to reduce cost and complexity, then receiver structure is simplified, but strong interference and out-of-band signals cause increased distortion and reduce headroom
Solution Approach 1:
The patent implements feedback by measuring the actual second order distortion produced by the amplifier under various operating conditions and using this information to adjust the transistor device sizing ratios. This closed-loop approach ensures that the amplifier maintains optimal linearity performance even when processing strong interference signals without an antenna filter.
Solution Approach 2:
The system performs preliminary measurements of distortion characteristics and stores correction data in a lookup table before normal operation. This allows the amplifier to be pre-configured with optimal transistor size ratios that will minimize distortion when exposed to strong out-of-band signals, effectively compensating for the removed antenna filter.
3Ease of manufacture
If single-ended input is used instead of differential input to save cost, then receiver cost is reduced, but even order non-linearity produces strong low frequency signals that reduce headroom
Solution Approach 1:
The patent changes the transistor device sizing parameters specifically for the single-ended input amplifier to compensate for the absence of differential cancellation. By optimizing the size ratio of the complementary transistor devices based on measured distortion characteristics, the system achieves low second order distortion in a cost-effective single-ended architecture.
Data Source
AI summary
An integrated circuit comprises a first amplifier circuit with a push-pull amplifier configured to be calibrated to a low second order distortion. The integrated circuit further comprises a second amplifier circuit with at least one push-pull amplifier, wherein a size ratio between sizes of the transistors is adjustable by adjusting the size of at least one transistor device. The size ratio can be consecutively adjusted to a plurality of values, and for each value, a first output signal of a push-pull amplifier with an applied test signal and a second output signal of a push-pull amplifier without applied test signal, are determined. The size ratio for which a difference between the push-pull amplifier output signals is closest to zero is determined, and the push-pull amplifier of the first amplifier circuit is calibrated in dependence of the determined size ratio.