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4.2.19.1 Receiver
The receiver section of MT6129 includes Quad-band low noise amplifiers (LNAs), RF quadrature
mixers, an on-chip channel filter, Programmable Gain Amplifiers (PGAs), quadrature second mixers,
and a final low-pass filter. The very low-IF MT6129 uses imagerejection mixers and filters to eliminate
interference. With accurate RF quadrature signal generation and mixer matching techniques, the image
rejection of the MT6129 can reach 35 dB for all bands. The fully integrated channel filters rejects
interference, blocking signals, and images without any external components.
Compared to a direct conversion receiver (DCR), MT6129's very low-IF architecture improves the
blocking rejection, AM suppression, as well as the adjacent channel interference performance.
Moreover, the very low-IF architecture eliminates the need for complicated DC offset calibration that is
necessary in a DCR architecture. In addition, the common-mode balance requirement of the SAW filter
input is relaxed. The MT6129 provides the analog IQ baseband output without any extra frequency
conversion components.
The MT6129 includes four differential LNAs for GSM 850 (869 MHz - 893 MHz), E-GSM 900 (925 MHz-
960 MHz), DCS 1800 (1805 MHz-1880 MHz) and PCS 1900 (1930 MHz - 1990 MHz). The differential
inputs are matched to 200 _ SAW filters using LC networks. The gain of the LNAs can be controlled
either high or low for an additional 35 dB dynamic range control. Following the LNAs are the image-
rejection quadrature RF mixers that down-convert the RF signal to the IF frequency. No external
components are needed at the output of the RF mixers.
The IF signal is then filtered and amplified through an image-rejection filter and a PGA.
The multi-stage PGA is implemented between filtering stages to control the gain of the receiver. With 2
dB gain steps, a 78 dB dynamic range of the PGA ensures a proper signal level for demodulation. The
quadrature 2nd mixers are provided on-chip to down convert IF signal to baseband in an analog
differential IQ format.
Copyright © 2007 LG Electronics. Inc. All right reserved.
Only for training and service purposes
4. Circuit Description
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LGE Internal Use Only
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