Mixer-First Receiver Circuit With Intrinsic Third-Harmonic Rejection
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Solution Overview
Problem
The Tayloe mixer scheme in radio receivers is susceptible to third harmonic interference due to the use of switches, which introduces spurious signals at baseband, necessitating the use of filters that limit the receiver's frequency range.
Innovation Solution
A mixer-first receiver design utilizing a single-pole, triple-throw (SP3T) switch driven by a local oscillator at three times the carrier frequency, combined with capacitors and an image-reject filter to intrinsically reject third harmonics without pre-filters, and a digital signal processor for further signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a Tayloe mixer scheme with switches is used, then the receiver achieves wide frequency range operation, but third harmonic interference creates spurious signals at baseband
Solution Approach 1:
The patent converts the harmful third harmonic interference into a beneficial filtering mechanism by using the third harmonic rejection property of the SP3T switch to inherently suppress spurious signals, thereby eliminating the need for external pre-filters and maintaining wide frequency range operation
2Object-generated harmful factors
If pre-filters are added to remove third harmonic signals, then spurious signal generation is prevented, but the receiver's frequency range is limited
Solution Approach 1:
The SP3T switch performs self-service by intrinsically rejecting third harmonic signals through its switching mechanism, eliminating the need for external pre-filters and thereby maintaining the receiver's wide frequency range capability while suppressing spurious signals
3Object-generated harmful factors
If a SP3T switch is used with LO frequency at three times carrier frequency, then third harmonic interference is intrinsically rejected, but the switching complexity increases
Solution Approach 1:
The patent changes the local oscillator frequency parameter to exactly three times the carrier frequency, which enables the SP3T switch to intrinsically reject third harmonic interference through its switching operation, achieving spurious signal suppression without adding external filtering components
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 design achieves inherent suppression of third harmonic interference, allowing the receiver to operate over a wider frequency range without pre-filters, maintaining high dynamic range and linearity.
Implementation Method 1
radio frequency (RF) signal are mixed to an intermediate frequency
Implementation Method 2
The LO frequency is three times the carrier frequency such that the RF port is sequentially switched to each of the 0-degree port, the 120-degree port, and the 240-degree port once during each period of the LO frequency
Implementation Method 3
The first capacitor is configured to low-pass filter the 0-degree port. The second capacitor is configured to low-pass filter the 120-degree port. The third capacitor is configured to low-pass filter the 240-degree port
Implementation Method 4
an image-reject filter coupled to the 0-degree port, the 120-degree port, and the 240-degree port. The image-reject filter is configured to output the baseband signal
Implementation Method 5
The receiver intrinsically rejects third-harmonics of the LO frequency in the RF signal
Data Source
AI summary
The mixer-first topology of receivers do not include low-noise amplifiers (LNA) preceding the mixer. The Mixer-First topology of radio receivers utilizes a direct-conversion quadrature mixer to down convert an RF signal to baseband, where a Hilbert Transform filter is used for sideband selection. When a switching mixer is used, the mixer-first receiver is capable of extremely high dynamic range and linearity. The downfall of the mixer-first topology is poor out-of-band signal rejection. A mixer-first receiver is described which achieves third-harmonic rejection without bandpass filtering proceeding the mixer.