TDA7514 STMicroelectronics, TDA7514 Datasheet - Page 70

• Manufacturer Part Number: TDA7514
• Description: SINGLE-CHIP FM/AM TUNER
• Manufacturer: STMicroelectronics

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TDA7514
5.4.13 AM MODE 2
In this operation mode the detector operates in a much more straightforward configuration: the instanta-
neous AM audio level is compared with a fixed programmable threshold, and the comparison result acti-
vates the retriggerable monostable. The advised programmed threshold corresponds to an equivalent
140% AM modulation level.
5.5 AUDIO PROCESSOR SECTION
5.5.1
The audio processor input section features a main channel multiplexer, a rear channel multiplexer (RSA,
Rear Seat Audio function), an input gain stage and autozero circuit.
The main channel multiplexer allows connecting the following sources to the main audio processing path:
The RSA selector (see speaker output section) can connect the rear speaker outputs to the following
sources bypassing all the tone and volume control:
The different sources are subjected to the following input attenuations:
The main channel signal path features an input gain stage (0..+15 dB, 1 dB step) to equalize the different
source levels and the autozero circuitry that removes the DC offset generated between the input pins and
the input gain stage output.
The autozero procedure is automatically run every time byte 0 of the audio processor I
dresses, that is every time the main source is changed or the input gain is changed. In case the new
source is the stereo decoder the source change must be preceded by opening the stereo decoder input
for a time long enough to discharge the stereo decoder internal filters (see stereo decoder input section).
The same is true even when the source is switched from AM to FM and vice-versa. The autozero proce-
dure can be manually activated through a dedicated bit, and can be prevented from running by setting a
different dedicated bit. The beep generator is considered a main channel source, and it can generate a
500 Hz, 1 kHz, 2 kHz, 3 kHz tone.
5.5.2
The input stage is followed by a soft mute stage aimed at automatically and smoothly driving the audio
processor from its current state into a full mute condition. The overall transition time is software selectable.
It is possible to control the stereo decoder RDS AF update mute circuits (input impedance open switch
("high ohmic mute"), stereo decoder mute and PLL hold) from the audio processor soft mute.
5.5.3
The TDA7514 features a loudness function made up by a 20 dB attenuator in 1 dB steps, a second order
LP filter with programmable corner frequency and a defeatable high pass filter with programmable corner
frequency.
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– 1 quasi-differential source;
– 1 stereo differential source;
– 1 mono differential source;
– tuner output (AM, FM);
– beep generator.
– 1 quasi-differential source;
– 1 stereo differential source;
– tuner output (AM, FM).
– quasi-differential source: -4 dB
– stereo differential source: 0 dB
– mono differential source: -4 dB.
INPUTS
SOFT MUTE
LOUDNESS FILTER
2
C software is ad-