RF Amplifier Limiter With Adaptive Threshold Feedback
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Solution Overview
Problem
Radio frequency integrated circuits (RFICs) face challenges in designing low noise amplifiers (LNAs) due to limited voltage handling, high noise, and interference from multi-standard systems and beam forming radios, which can damage amplifiers and degrade communication, especially in scenarios like small cell base stations and beam forming radios where high power out-of-band signals can enter without filtering.
Innovation Solution
An amplification device comprising an amplifier circuit and a limiter with a differential amplifier, diodes, and a feedback stage that adjusts the threshold for limiting based on feedback signals to protect the amplifier from damage while minimizing signal degradation, allowing for adaptive threshold control and gain management to handle peak power levels and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If filtering is minimized at the input of the receiver to reduce cost, then cost is reduced, but crosstalk may cause high signal levels inside LNAs and damage them
Solution Approach 1:
The limiter circuit is placed before the LNA to preemptively clamp high signal levels from interferers before they can damage the LNA. This preliminary protective action allows the system to operate without expensive input filtering while maintaining amplifier safety.
Solution Approach 2:
The limiter circuit acts as an intermediary protective element between the antenna input and the LNA. It mediates the signal levels, allowing high power interferers to be safely attenuated before reaching the sensitive LNA, thus enabling cost-effective designs without input filters.
2Reliability
If limiting is applied continuously to protect the amplifier, then amplifier protection is improved, but signal quality degrades due to constant limiting
Solution Approach 1:
The limiter threshold is made dynamic through feedback control. The threshold adapts based on the operating conditions and signal levels, enabling the limiter to remain inactive during normal operation (preserving signal quality) while automatically activating when high power interferers are detected (providing protection).
Solution Approach 2:
A feedback mechanism monitors the signal levels and adjusts the limiter threshold accordingly. This feedback control ensures the limiter only activates when necessary to protect the amplifier, avoiding unnecessary signal distortion and maintaining high signal quality during normal operation.
3Reliability
If high gain is used in the LNA to suppress noise, then noise suppression is improved, but the amplifier becomes more susceptible to damage from high signal levels
Solution Approach 1:
The limiter is positioned to act before the high-gain LNA, preemptively clamping high signal levels that would otherwise be amplified and potentially damage the amplifier. This allows the LNA to operate at high gain for noise suppression without the increased susceptibility to damage.
4Device complexity
If no filters are used in beam forming radios to maintain high antenna count, then device complexity is reduced, but high power out-of-band signals may enter the LNA and damage it
Solution Approach 1:
The limiter serves as a protective intermediary in beam forming radio systems, enabling the use of numerous antennas without complex filtering. It blocks high power out-of-band signals before they can damage the LNAs, maintaining system simplicity while ensuring amplifier protection.
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 solution provides effective protection against damage to the amplifier circuit by applying limiting only when necessary, maintaining signal quality, and enabling operation over a wide dynamic range without significant hysteresis or transient signals, thus enhancing the reliability and performance of RFICs in challenging environments.
Implementation Method 1
a first diode having a first anode coupled to the first signal output and a first cathode coupled to the differential amplifier output
Implementation Method 2
a differential amplifier comprising a first differential amplifier input for a threshold control signal, a second differential amplifier input for a feedback signal, and a differential amplifier output for a threshold signal indicative of a difference between the threshold control signal and the feedback signal
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
An amplification device (100) comprises an amplifier circuit (110) and a limiter (120). The amplifier circuit (110) comprises a signal input (111 ) for an input signal to be amplified and a first signal output (112) for a first output signal. The limiter (120) comprises a differential amplifier (125) comprising a first differential amplifier input (129) for a threshold control signal, a second differential amplifier input (113) for a feedback signal, and a differential amplifier output (124) for a threshold signal indicative of a difference between the threshold control signal and the feedback signal. The limiter (120) also comprises a first diode (121) having a first anode (122) coupled to the first signal output (112) and a first cathode (123) coupled to the differential amplifier output (124), and a feedback stage (128) coupled between the differential amplifier output (124) and the second differential amplifier input (113). The feedback stage (128) is arranged to generate the feedback signal dependent on the threshold signal.