Segmented RF Loopback Conductor for Low-Parasitic IP2 Calibration
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Solution Overview
Problem
Existing methods for measuring and calibrating the second-order intercept point (IP2) of cellular telephone transceivers are inefficient, as they often require external power amplifiers, consume excessive power, and may introduce nonlinearities due to long on-chip loopback connections, making it difficult to account for temperature and voltage variations during operation.
Innovation Solution
An RF transceiver integrated circuit with a novel segmented, low parasitic capacitance internal loopback conductor circuit that uses a current mode output mixer and a passive mixer with a transimpedance amplifier, allowing for self-testing and calibration by driving a two-tone current signal through a single quadrature branch, reducing power consumption and minimizing parasitic loading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external power amplifiers are used for IP2 measurement, then measurement capability is improved, but power consumption increases and device complexity increases
Solution Approach 1:
The transceiver uses its own internal power amplifier and receiver components to perform IP2 self-testing, eliminating the need for external power amplifiers. The transmitter generates test tones and the receiver measures the second-order distortion products, allowing the device to self-diagnose and self-calibrate without external testing equipment.
Solution Approach 2:
The power amplifier serves dual functions: normal signal transmission and test tone generation for IP2 measurement. The receiver similarly performs both normal reception and distortion measurement during self-testing, reducing the need for dedicated test equipment.
2Ease of operation
If long on-chip loopback connections are used, then internal testing is enabled, but nonlinearities are introduced due to parasitic capacitance
Solution Approach 1:
The loopback connection is divided into multiple segments with switching capability. The transmitter can connect to different receiver paths through controlled switches, allowing selective activation of loopback paths. This segmentation enables internal testing while minimizing the length of active conductors to reduce parasitic effects.
Solution Approach 2:
The loopback connection uses dynamic switching to activate only the necessary signal paths during self-testing. By controlling switches based on test requirements, the system dynamically configures the loopback path length and topology, minimizing parasitic capacitance effects while enabling comprehensive internal testing.
Data Source
AI summary
An RF transceiver integrated circuit has a novel segmented, low parasitic capacitance, internal loopback conductor usable for conducting IP2 self testing and/or calibration. In a first novel aspect, the transmit mixer of the transceiver is a current mode output mixer. The receive mixer is a passive mixer that has a low input impedance. In the loopback mode, the transmit mixer drives a two tone current signal to the passive mixer via the loopback conductor. In a second novel aspect, only one quadrature branch of the transmit mixer is used to generate both tones required for carrying out an IP2 test. In a third novel aspect, a first calibration test is performed using one quadrature branch of the transmit mixer at the same time that a second calibration test is performed using the other quadrature branch, thereby reducing loopback test time and power consumption.