QN8007B/8007LB
4.4 Audio Processing
The QN8007 supports audio AGC, programmable pre-emphasis, and soft clipping. The AGC state machine will detect
the signal level and control the VGA gain to optimize both SNR and THD. A saturation indicator is also integrated which
will be asserted when the input signal is out of the range of AGC. A soft clipping feature provides graceful performance
degradation when the signal level is higher than a pre-determined level.
Stereo signal is generated by the MPX circuit. It combines the left and right channel signals in the following way:
m(t) L(t) R(t) L(t) R(t) sin(4 ft 2 ) sin(2 ft ) d(t)sin(6 ft 3 )
0
0
0
Here, L(t) and R(t) correspond to the audio signals on left and right channels respectively, f = 19 kHz, is the initial phase
of pilot tone and is the magnitude of pilot tone, and d(t) is RDS signal. In mono mode, only the L+R portion of audio
signal is transmitted. The 19 kHz pilot tone is generated by the MPX circuit which contributes 9% of peak modulation,
and RDS signal will contribute 2.1% of peak modulation.
A pre-emphasis function is also integrated with both 75s and 50s time constants. The time constant can be programmed
through the serial control interface.
4.5 Channel Setting
The QN8007 supports both clear channel scan and manual channel setting.
Manual Channel Setting
By programming channel index CH[9:0], the RF channel can be set to any frequency between 76 MHz ~ 108 MHz in 50
kHz steps. The channel index and RF frequency have the following relationship:
FRF = (76 + 0.05 x Channel Index), where FRF is the RF frequency in MHz.
The QN8007 has an integrated crystal oscillator and supports various crystal frequencies. Alternatively, the QN8007 can
be driven externally by various clock frequencies.
Clear Channel Scan
The QN8007 can automatically find the clearest channel and return the channel information for FM transmission. The
start, stop and frequency step of searching as well as upward or downward searching can be programmed through serial
interface.
Rev 2.09 (11/09)
Confidential A
Copyright ©2009 by Quintic Corporation
Confidential Information contained herein is covered under Non-Disclosure Agreement (NDA).
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