Double-Balanced Mixer Balun RC Network for Higher Linearity
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Solution Overview
Problem
Double balanced mixers face challenges in achieving high linearity and conversion gain while maintaining port isolation and bandwidth, with existing solutions often compromising on one or more of these parameters.
Innovation Solution
Incorporating an RC network between the ports of the balanced output of a balun and either ground or a common mode node improves linearity and port isolation without affecting other performance aspects, using hybrid Marchand/back-wave baluns that adapt frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If various techniques are used to improve linearity (such as RLC circuits, capacitor filters, resistor loads, tunable capacitors), then output IP3 is improved, but conversion gain, port-to-port isolation, or operating bandwidth deteriorate
Solution Approach 1:
An RC network is introduced as an intermediary element between the balun output and ground/common mode node. This RC network acts as a mediator that improves linearity by controlling signal paths without directly interfering with the mixing process, thereby avoiding the trade-offs of previous techniques that directly modified the mixing core or signal paths.
Solution Approach 2:
The invention changes the electrical parameters of the balun output stage by adding the RC network, which modifies the impedance characteristics and signal distribution. This parameter change improves linearity by 2 dB and isolation by 3 dB without significantly affecting conversion gain, as the RC time constant is designed to be appropriate for the operating frequency range.
2Manufacturing precision
If RLC resonant circuits are used to improve linearity at a specified narrow frequency band, then output IP3 is improved, but operating bandwidth deteriorates
Solution Approach 1:
The invention uses an RC network instead of an RLC resonant circuit, changing the frequency-selective parameter from resonant (which creates narrow bandwidth) to RC time-constant based (which provides broader bandwidth). The RC network's frequency response is determined by the time constant τ=RC, which can be designed to provide linearity improvement across a wide frequency range rather than at a single resonant frequency.
Solution Approach 2:
The invention replaces the complex RLC resonant circuit with a simpler RC network that achieves the linearity improvement function with fewer components and less stringent design constraints, effectively using a simpler structure to achieve the desired performance over a broader bandwidth.
3Manufacturing precision
If parallel RC network is used to shape LO input signal waveform, then linearity is improved, but port-to-port isolation and balance operation deteriorate
Solution Approach 1:
The RC network is positioned as an intermediary between the balun output and ground, rather than being inserted in the signal path between ports. This intermediary placement allows it to shape waveforms and improve linearity without directly interfering with the balance operation or port-to-port isolation, as it does not disrupt the differential signal paths.
4Adaptability or versatility
If distributed element baluns are used to provide wide-band differential signals, then operating bandwidth is improved, but circuit area and manufacturing cost increase
Solution Approach 1:
The invention uses lumped-element baluns with dynamic RC networks instead of static distributed elements. The RC networks provide frequency-dependent impedance transformation that mimics the wide-band behavior of distributed elements but in a compact lumped-element configuration, achieving wide bandwidth without the large physical footprint of transmission line structures.
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 output IP3 by 2 dB and LO to RF isolation by 3 dB across the entire bandwidth, maintaining conversion gain and improving overall mixer performance.
Implementation Method 1
uses a parallel RC network coupled in series of the in-phase gates of a mixing transistor to shape the wave form of the LO input signal with reduced rise and fall times at the mixing transistor gates
Implementation Method 2
proposed to improve linearity by using a capacitor as a filter connecting the input and output ports and by using a resistor as a load to absorb the spurious between the input and output ports
Implementation Method 3
is one example of double balanced mixer with resonant resistor-inductor-capacitor (RLC) circuit across the balanced output ports of the mixer balun, which provide better linearity and IP3 at a specified narrow frequency band because of the resonant nature of the RLC network
Data Source
AI summary
An improved double balanced mixer is provided which in one embodiment includes a first balun for receiving a first single input and providing a first balanced output having two ports, a second balun for receiving a second single input and providing a second balanced output having two ports, and a balanced mixer core responsive to the first and second balanced outputs to provide a mixed signal from the first and second single inputs. The first balun includes an RC network coupled between at least one of the ports of the first balanced output and one of ground and a common mode node of the first balun to improve the linearity of the double balanced mixer.