RF Electronics Chapter 5: Frequency Mixers Page 163
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 5.90. Mini-Circuits IQ mixers. [15]
Active IQ Mixers
For cellular base stations, radio and TV transmitters, and their test equipment, IQ
modulation is used to produce the complex modulated waveforms used in modern
communication systems. The mixers used in such signal generators are often active
(Frater-Gilbert cell) IQ mixers. Computer controlled DC bias (control and calibration)
signals are used to ensure that the carrier feed-through, quadrature phase shifts and I and
Q gains are correct. The design of such IC's can cost more than one million dollars. For
large-scale applications, such as cellular base stations or automotive distance and
collision detection radars, commercial IQ modulator and demodulator IC's are available.
IQ demodulators allow a zero IF frequency to be used, by placing the LO at the centre of
the RF band, and producing I and Q baseband outputs, which are passed through simple
low pass filters before being digitised. This avoids the need for bulky IF filters. The
required filtering is then done digitally, allowing very frequency selective filtering to be
achieved.
Image Reject Mixers
Figure 5.91. Image reject mixer (up converter).
RF Electronics: Design and Simulation
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