Pad Attenuator Circuit for Receiver Linearity and Low PA Loading
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Solution Overview
Problem
Conventional attenuators in wireless devices have a limited ceiling for receive linearity due to preceding circuitry limitations, especially when transmitter and receiver share pad circuitry, leading to non-linearity and degradation of signal quality.
Innovation Solution
A pad attenuator is integrated on the semiconductor die, sharing a blocking capacitor with the power amplifier and operating with different voltage regulators in transmit and receive modes, using programmable resistors and MOSFET switches to provide adjustable attenuation and protect the receiver circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional attenuator is used to reduce signal level of blocking signals, then the signal attenuation is achieved, but the receiver linearity is limited due to preceding circuitry in the lineup
Solution Approach 1:
The attenuator function is segmented into two parts: a conventional RF attenuator for initial attenuation and a pad attenuator for additional attenuation. This segmentation allows each attenuator to operate in its optimal range, with the pad attenuator specifically targeting strong blocking signals that pass through the first attenuator, thereby improving overall receiver linearity while maintaining signal attenuation capability
Solution Approach 2:
The pad attenuator acts as an intermediary element inserted between the antenna and the receiver lineup. This intermediary component provides an additional attenuation stage that specifically addresses the linearity limitation caused by preceding circuitry, allowing the system to achieve both signal attenuation and improved receiver linearity
2Area of stationary object
If receiver and transmitter share pad circuitry, then chip real estate is reduced, but additional circuitry at the pad degrades the impact of the attenuator
Solution Approach 1:
The pad attenuator is designed to be dynamically controlled with different attenuation levels for transmit and receive modes. During transmit mode, the pad attenuator provides minimal attenuation to avoid degrading the PA output. During receive mode, it provides high attenuation to improve receiver linearity. This dynamic operation allows sharing of pad circuitry while maintaining attenuator effectiveness
Solution Approach 2:
The attenuation parameter of the pad attenuator is changed based on operating mode. In transmit mode, the attenuation is set to a low value to minimize impact on PA performance. In receive mode, the attenuation is increased to maximize linearity improvement. This parameter change allows the same circuitry to serve both functions effectively
3Reliability
If the pad attenuator attenuates receive RF signal, then receiver linearity is improved, but the PA load is increased in transmit mode
Solution Approach 1:
The pad attenuator's attenuation value is dynamically adjusted based on whether the system is in transmit or receive mode. During transmit mode, the attenuation is minimized to reduce loading on the PA. During receive mode, the attenuation is maximized to improve receiver linearity. This dynamic adjustment resolves the contradiction between improving receiver linearity and minimizing PA loading
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 enhances receiver linearity by directly attenuating blockers at the input pad, minimizing voltage stress on subsequent circuits and improving overall signal quality while reducing chip real estate.
Implementation Method 1
a blocking capacitor formed on the semiconductor die coupled to the output node of the PA
Implementation Method 2
a programmable resistor; and at least one switch coupled to the programmable resistor
Data Source
AI summary
In one aspect, an apparatus comprises: a low noise amplifier (LNA) to receive and amplify a receive radio frequency (RF) signal; a power amplifier (PA) to amplify a transmit RF signal and output the amplified transmit RF signal at an output node of the PA; a blocking capacitor coupled to the output node of the PA; an input/output (I/O) pad coupled to the output node, the I/O pad to interface with an antenna; and a pad attenuator coupled to the output node of the PA, the pad attenuator to attenuate the receive RF signal in a receive mode and minimize a load on the PA in a transmit mode.