1. Top 7 Ways to Create a Quadrature (90˚) Phase Shift

We’ve talked a lot about IQ mixers in the last few posts, about their theoretical underpinnings and applications as a phase detector and phase modulator. In upcoming posts we will discuss applications of image reject and single sideband mixers as well. The key to all of these circuits is the quadrature phase shift, both at the LO side for an IQ mixer, and at the LO and IF side for an image reject or single sideband mixer.

Remember: a phase shift is not the same as a time shift. This is one of the most difficult concepts to grasp in RF, microwaves, and optics. We will begin with the trivial example of a time delay, just to show that this doesn’t work for anything but the most simple circumstances. We go on to show how different techniques can be used to create more flexible and useful quadrature phase shifts to ultimately realize our goal of an ideal, broadband IQ/image reject/single sideband mixer. Read More…

2. The Why and When of IQ Mixers for Beginners

Sometimes you need a mixer; sometimes you need an IQ mixer. How do you know which one to buy? Before answering this question, I recommend reading the Mixer Basics Primer to get a good understanding of the fundamentals of mixers, the blog post ‘IQ, Image Reject, and Single Sideband-Mixers’ for and introduction to these mixers, and ‘How to think about IQ mixers’ if you want a deeper physical understanding of the mechanisms of IQ, image reject (IR), and single sideband (SSB) mixers. Read More…

3. How to think about IQ mixers

There are many ways to think about IQ modulation, and all of them rely on math. This is because ‘quadrature’ modulation is a mathematical construct, a way of thinking about how time domain signals can be manipulated more than a physical reality. In this blog post I will describe how I think of IQ modulation, which is as the cancellation of a signal through two 90° phase shifts that create a 180° phase shift, which is the negative of the original signal. The negative and positive versions of the signals cancel, resulting in suppression of the other signal. This is identical to the math that governs image cancellation in image reject and single sideband mixers, the only difference is that one of the 90° phase shifts occurs at the transmitter in an IQ scheme, while they are both at the receiver in the image reject/single sideband scheme. Read More…

4. How to Measure Mixer IP3 and Identify Potential Error Sources

Mixer linearity is continuously and permanently a critical problem faced in RF system design. The nonlinear action of all physically realizable RF mixers propagates throughout signal chains generating undesired, unfilterable output harmonics, multitone intermodulation, and nonrecoverable nonlinear signal distortion. For example, nonlinear mixing action can cause undesired output harmonics (i.e., spurs) such as the $2f_{RF} \times 2f_{LO}$ or the $2f_{RF} \times f_{LO}$ spur instead of the desired $f_{RF} \times f_{LO}$ converted signal. In multitone applications, such as data transmission and radar tracking, mixing heavily exacerbates the problem of spectral purity by not only introducing a second set of unwanted, unfilterable output harmonics but by also introducing multitone intermodulation distortion (IMD). IP3, or the 3rd order intercept point (TOI), is the figure of merit by which industry judges the linearity of all active, power-consuming RF components and their ability to maintain core linear assumptions about circuits. The mixer is no exception. Read More…

5. All About Mixers as Phase Detectors

Some of the most common questions we receive here are about using mixers as phase detectors. We previously discussed this topic in the post, “DC Offset and Mixers as Microwave Phase Detectors”. In this post we will go into much further depth about the physical mechanisms by which mixers act as phase detectors, and what is important for engineers trying to accomplish this in the lab. First a warning though: we’re just showing experimental results here. The real experts in phase detectors, phase noise, and all things related to phase are the people that do this every day at Holzworth Instrumentation. Read More…

6. 6 Ways to Make an N-Way Power Splitter

One of the unique products that we have at Marki Microwave is our broadband, high isolation 3-way and 4-way power dividers. In this blog post we will answer some common questions we receive, including:

• How to make a 5 way power divider
• How to make a 6 way power divider
• How to make a 7 way power divider
• How to make an 8 way power divider
• How to make a 10 way power divider
• How to make a 12 way power divider
• How to make a 16 way power divider
• How to make a 32 way power divider
• How to make an way power divider

7. Current vs. Voltage Baluns

When reading in the literature on the internet about baluns, a distinction that will often come up is ‘current’ baluns vs. ‘voltage’ baluns. I’ve always found this distinction confusing, because an electromagnetic wave converted by a balun from differential to unbalanced modes consists of both current AND voltage waves. They interplay to make a single electromagnetic wave. I can understand the terms applied to transistors, i.e. the current driven BJT vs. the voltage driven FET, since in this case the charges are either transmitted across the junction (current) or they only create a field (voltage). Read More…

8. An Introduction to Microwave Amplifiers Part 1: Microwave Amplifier Applications

This is a (virtually) math-free introduction to microwave amplifiers from an applications standpoint. There are many references available for the aspiring amplifier designer; this series of posts will attempt to quickly elucidate the relevant factors for the RF system design engineer working to evaluate the appropriate amplifier for her system design.

Types of Microwave Amplifiers

9. IQ, Image Reject, and Single-Sideband Mixers

IQ and Image Reject or Single Sideband mixers use similar circuitry to solve two different fundamental problems in communications and signal processing. IQ mixers address the problem of maximizing information transmission by allowing the user to modulate both the in-phase and quadrature components of a carrier simultaneously, multiplexing two signals onto the carrier*. Image Reject (IR) mixers allow a user to select a signal in a crowded signal environment while suppressing the adjacent image signal, relaxing receiver filtering requirements. Single Sideband (SSB) mixers allow a user to upconvert a signal onto a carrier while suppressing the same image frequency signal, relaxing transmitter filter requirements. Read More…

10. How do amplifiers affect signal phase noise?

Phase noise is critical to systems, like Electronic Warfare and 5G Communications, requiring precise frequency stability. Oscillators are typically the determining factor in the signal chain’s phase noise performance. However, in extremely low phase noise systems, the amplifier phase noise contribution is considered. This tech note explores amplifier’s phase noise contribution, demonstrating:

• Amplifiers only contribute 1/f and White PM noise to a signal chain.
• 1/f noise is apparent at approximately 1‑100 kHz offset frequencies.
• Amplifier 1/f noise adds linearly in series and subtracts linearly in parallel.
• Oscillator higher order phase noise dominates at <1 kHz offset frequency.