Interleaved Switching Mixer Clocking to Eliminate LO Delay Mismatch
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Solution Overview
Problem
Conventional switched-mode mixers in RF transmitters face performance impairments due to propagation delays in local oscillator signals, especially at higher frequencies, which affect the suppression of carrier and sideband frequencies.
Innovation Solution
A high-frequency transmit circuit generates matched differential interleaved local oscillator signals using a quadrature generator and frequency divider circuit, eliminating inherent imbalances and propagation delays by selectively passing pulses through a switching mixer with a matched switching topology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional switched-mode mixers use interleaved local oscillator signals, then the mixer can achieve improved noise and linearity performance, but propagation delays in the generated local oscillator signals impair mixer performance
Solution Approach 1:
The patent divides the local oscillator signal generation into separate matched paths for in-phase and quadrature components. Each path is segmented to have identical circuit topology, ensuring that propagation delays are equalized across both paths. This segmentation allows the mixer to receive synchronized local oscillator signals without the timing mismatches that would otherwise degrade performance.
Solution Approach 2:
The patent intentionally introduces asymmetry in the form of matched delay elements that compensate for inherent path differences. By adding equal delay to both in-phase and quadrature local oscillator paths, the system creates a symmetric timing relationship despite asymmetric physical routing, thereby eliminating propagation delay mismatches that would impair mixer operation.
2Productivity
If higher frequency transmitters are used to support high-bandwidth applications, then data transmission capability is improved, but propagation delay issues become more problematic
Solution Approach 1:
The patent changes the timing parameters of the local oscillator signals by introducing matched delay elements. These delay elements are designed to equalize the propagation delays in both signal paths, ensuring that even at higher frequencies where timing is critical, the in-phase and quadrature components arrive simultaneously at the mixer. This parameter adjustment allows high-frequency operation without suffering from propagation delay mismatches.
3Device complexity
If resistive summation is used to combine I and Q signals, then the mixing operation is simplified, but 50% efficiency loss occurs
Solution Approach 1:
The patent replaces the resistive summation mechanism with a switched-mode combining approach. Instead of using resistors to algebraically combine the in-phase and quadrature signals (which dissipates 50% of the power), the invention uses electronic switches controlled by local oscillator signals to time-multiplex the combination. This substitution eliminates the inherent efficiency loss of resistive networks while maintaining the simplicity of the mixing operation.
Data Source
AI summary
An integrated transmit circuit includes a voltage controlled oscillator (702) for generating an input frequency signal (e.g., VCO) that is provided to a divide by two quadrature generator circuit (706) which generates therefrom in-phase and quadrature clocking signals (I, IB, Q, QB) that are applied to control a plurality of transmission gates (711-718) configured in a matched switching topology (710) so as to selectively pass pulses from the input frequency signal, thereby generating interleaved LO pulses (Ø1, Ø1B, . . . Ø4, Ø4B). By applying the interleaved LO pulses to control the transmission gates (26, 28, 30, 32, 34, 36, 38, and 40) in the upmixer (720), the +I, −I, +Q, −Q input signals are interleaved over a plurality of phases of a carrier period to produce differential outputs (42, 44).