Active-Integrated Self-Oscillating Image Reject Mixer (IRM)
A conventional image reject mixer (IRM) is composed of an antenna, a radio frequency (RF) hybrid coupler, low noise amplifiers (LNAs), an external local oscillator (LO), mixers, intermediate frequency (IF) filters, and an IF hybrid coupler. The usage of the RF hybrid coupler and the external LO i...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2018
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| Subjects: | |
| Online Access: | http://eprints.usm.my/47341/1/Active-Integrated%20Self-Oscillating%20Image%20Reject%20Mixer%20%28IRM%29.pdf |
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| Summary: | A conventional image reject mixer (IRM) is composed of an antenna, a radio
frequency (RF) hybrid coupler, low noise amplifiers (LNAs), an external local
oscillator (LO), mixers, intermediate frequency (IF) filters, and an IF hybrid coupler.
The usage of the RF hybrid coupler and the external LO in the conventional IRM not
only consume large space, the interconnections for the LO to the mixer as well as the
interconnections for the RF hybrid coupler with the antenna and the mixer also result
in losses. These drawbacks eventually affect the performance of the overall system.
In view of these concerns, this research introduces a new architecture that eliminates
the need of the RF hybrid coupler and external LO, entitled ‘Active-Integrated Self-
Oscillating Image Reject Mixer (AISOIRM)’. The objectives of this research are to
embed an active integrated antenna (AIA), a self-oscillating mixer (SOM), an IRM
together into a single platform, and subsequently to implement, to characterize, as
well as to evaluate the design in ensuring its performance is compatible with that of
the conventional IRM. As a proof-of-concept work, this research realizes the
AISOIRM architecture that operates in the 2.4 GHz Industrial, Scientific, and
Medical (ISM) band. Its RF is assigned at 2.4 GHz and its LO frequency is 2.5 GHz.
With this, the down-converted IF is 100 MHz. Two different topologies are designed.
One adopts an E-shaped active antenna which supports an in-phase RF power divider
function, namely the E-Topology. The other uses an F-shaped active antenna which
supports a quadrature-phase RF power divider function, namely the F-Topology.
Each of these topologies is configured in two different ways. The first configuration
embeds both the antenna and IRM directly. Thereby, the configuration with the Eshaped
antenna is named as ‘E-AISOIRM’ while the configuration with the F-shaped
antenna is called ‘F-AISOIRM’. The second configuration cascades the amplifiers
between the antenna and the IRM to increase the RF and LO signal levels that are
delivered into the mixer. Thereby, the configuration with the E-shaped antenna is
named as ‘E-Amp-AISOIRM’ while the configuration with the F-shaped antenna is
called ‘F-Amp-AISOIRM’. The AISOIRM architecture eliminates the need of the RF
hybrid coupler and external LO mainly by resonating its AIA at both the RF and LO
frequencies. Aside from functioning as a passive radiator, the antenna also functions
as an RF power divider, which replaces the need of the RF hybrid coupler.
Correspondingly, the SOM is formed by merging the LO port of the antenna with the
LO path of the IRM and the core mixer. This way, the LO signal is received from the
antenna and injected into the mixer. Hence, the external LO source is omitted. To
initiate the AISOIRM research, relevant literatures are first reviewed. This is
followed by the theoretical calculations and simulations of the designs. During the
theoretical calculations, the phase cancellation mechanism of both the E-AISOIRM
and F-AISOIRM are analyzed mathematically. After this, all the four AISOIRM
designs along with the antennas and sub-circuit designs are simulated using
Advanced Design System (ADS). Three levels of simulation are performed. The
ideal block design simulation performs a preliminary analysis on the overall designs,
the circuit design simulation verify the schematics of the designs, and the circuitlayout
design simulation finalizes the designs by taking into account the simulated
effects of the layouts and printed circuit boards (PCBs) on the circuit designs. The
finalized designs are then implemented, whereby the prototypes are assembled and
characterized. The results obtained from the evaluations are subsequently analyzed.
It is noted that the measured image rejection ratio (IRR) obtained for all the designs
are greater than 15 dB, when biased near to the mixer transistor pinch-off at 0.7 V
and supplied with the LNA optimum bias at 2.5 V. According to its measured results,
the IRRs for the E-AISOIRM and the E-Amp-AISOIRM are 20.84 dB and 22.28 dB,
respectively. Meanwhile, the measured IRRs for the F-AISOIRM and the F-Amp-
AISOIRM are 21.72 dB and 21.52 dB, respectively. Generally, comparing between
both the topologies, the E-Topology is preferred due to its much stable RF phase
distribution, which thereon yields a much robust system. This is because the 0o RF
phase division from the E-shaped antenna is determined by the symmetric geometry
of its antenna structure. In converse, the 90o RF phase division of the F-shaped
antenna depends on the exactness of its geometrical dimensions and the positions of
its feed points instead. Hence, the RF phase of the F-shaped antenna is much
sensitive to distortion than the RF phase of the E-shaped antenna. In overall, the
AISOIRM architecture is able to perform image rejection with less external injection
and more on self-operation through internal mechanism that contributes to more
compact design. Therefore its miniaturized size is well suitable for wireless RF
applications. |
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