I/Q (Inphase and quadrature) demodulation circuit

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In summary, the conversation is about building an I/Q demodulation circuit that operates at 20MHz. The person is asking for advice on what opamp and mixer to use, as they are unsure where to start. They mention finding an AD8333 chip on the Analog Device website, but are concerned about its small size and how to incorporate it onto a PCB. The other person suggests using a split LO and two mixers to create a demodulator, and coding on an MCU for the rest. The conversation also touches on the trend of smaller chips in the industry for digital demodulation.
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kent
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Hi guys

I want to build a I/Q demodulation circuit...operate at 20MHz...does anyone have any experience on building this circuit in a similar frequency range? what kind of opamp + mixer shall I go for? There are too many parts I don't even know where to start from...

I hav browsed through the Analog Device website and seems like there is an AD8333 chip that can do the trick for me...but the problem is that the size of the chip is extremely small...(5mm x 5mm)...and I don't know how to put that on a PCB...

here is the link to the AD8333 chip: http://www.analog.com/en/prod/0%2C28...8333%2C00.html

Thanks!
 
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Yea those chips are even smaller than SMT, and can only be soldered with robotic machines on an assembly line. As the industry pushed the envelope with digital demodulation, small chips are very common.

But for 20 MHz, you could cook up small demodulator using a split LO by 90 degrees and feed them to two mixers whose RF input is evenly split. The IF's would need to be hooked up to two ADC's. Then rest is coding on an MCU or what not.
 
  • #3


Hi there,

Building an I/Q demodulation circuit can be a challenging task, especially when operating at a high frequency of 20MHz. I would recommend starting by doing some research on the basics of I/Q demodulation and the different components involved in the circuit.

As for the opamp and mixer, it really depends on your specific application and the performance requirements. I would suggest looking for opamps and mixers that have a high bandwidth and low noise figure to ensure accurate demodulation at 20MHz. You can also consult with a specialist at Analog Devices for recommendations on suitable components for your circuit.

Regarding the AD8333 chip, it seems like a suitable option for your application. The small size may be a challenge, but there are techniques for mounting small chips on a PCB, such as using a breakout board or using a solder paste stencil. You can also consult with a PCB manufacturer for assistance in designing a PCB that can accommodate the AD8333 chip.

I hope this helps and good luck with your project!
 

What is I/Q demodulation and why is it important in communication systems?

I/Q (Inphase and quadrature) demodulation is a technique used to extract the original information signal from a modulated carrier signal. It involves separating the components of the carrier signal into two orthogonal components - inphase and quadrature - and using them to retrieve the original signal. This technique is important in communication systems as it allows for efficient and accurate transmission of information signals over a carrier signal.

How does an I/Q demodulation circuit work?

An I/Q demodulation circuit typically consists of a mixer, low-pass filters, and a phase shifter. The mixer multiplies the modulated signal with a local oscillator signal to extract the inphase and quadrature components. The low-pass filters then separate and filter the two components, and the phase shifter adjusts the phase of one of the components to be in quadrature with the other. The two components are then combined to retrieve the original signal.

What are the advantages of using I/Q demodulation?

I/Q demodulation offers several advantages over traditional amplitude demodulation techniques. It allows for better suppression of noise and interference, as well as a higher signal-to-noise ratio. It also enables the transmission of multiple signals simultaneously over the same carrier frequency, making it a more efficient use of bandwidth.

What are some applications of I/Q demodulation?

I/Q demodulation is commonly used in many communication systems, including wireless communication, satellite communication, and digital television broadcasting. It is also used in radar systems for target detection and tracking, and in medical imaging for signal extraction from modulated signals.

Are there any limitations to using I/Q demodulation?

I/Q demodulation is not suitable for all types of modulated signals, as it requires a carrier signal with a constant amplitude and phase. It also requires precise synchronization between the local oscillator and the modulated signal, which can be challenging in certain environments. Additionally, the complexity of the circuit may make it more expensive to implement compared to other demodulation techniques.

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