SAA7806H NXP [NXP Semiconductors], SAA7806H Datasheet - Page 23

• Manufacturer Part Number: SAA7806H
• Description: One chip automotive CD audio device
• Manufacturer: NXP [NXP Semiconductors]

Philips Semiconductors
9397 750 13697
Objective data sheet
Fig 15. AGC and AOC loops
6 MSBs
4 MSBs
G1
INTEGRATOR
INTEGRATOR
HIGH-PASS
(ANALOG)
FILTER
The minimum and maximum peaks of the incoming signal are measured during a
programmable window period. The highest and lowest value samples within this window
are used to update maxpeak and minpeak.
The window width of the measurement is controlled via
AGCAOCControl(PDMEASWINDOW).
AGC and AOC control block:
input of the ADC by controlling the gain of an on-chip analog gain amplifier. The AOC
control block controls the RF offset at the input of the ADC by adding or subtracting offset
just before the ADC. Both AGC and AOC loops are built up in the same manner and are
pictured in
First, the maximum and minimum peaks on the envelope of the RF signal after the ADC
are measured via a noise filter and the window peak detector (see
detectors” on page
the offset as (maxpeak + minpeak) / 2.
For tuning the loops, it is possible to read back the HFMaxPeak, HFMinPeak,
HFAmplitude and HFOffset, as measured by the decay peak detector, from registers.
AGC control:
in the analog part: G1 (fixed) and G2 (dynamic). G1 has a gain-range from 0 dB to 24 dB
in 16 steps of 1.6 dB, while G2 has a range from 0 dB to 12 dB in 16 steps of 0.8 dB. Both
gains can be programmed via register AGCGain. G1 will stay fixed, while G2 can be
regulated in hardware as soon as the AGC is turned on.
The AGC will regulate the gain such that the measured amplitude stays between a
programmed upper threshold (AGCThrHi) and lower threshold (AGCThrLo). If amplitude
is smaller, gain will increase; if amplitude is too large, gain will decrease. Whenever
clipping is detected on one or two sides, gain will decrease as well. These gain changes
are not sent to the analog gain amplifier directly, but are integrated over time. Only if on
average a gain increase or decrease is requested, this will result in a real gain increase or
decrease on the amplifier (the gain can also be read back via register AGCGain).
K-offset
K-gain
G2
Figure 15
software/
software/
The RF-amplitude at the ADC input can be changed with 2 gain amplifiers
defect
defect
21). After that, the amplitude is calculated as maxpeak minpeak, and
1
1
1
1
with their relative position within the signal conditioning block.
HI
LO
HI
LO
Rev. 01 — 20 June 2005
G3
CLIPPING
DETECT
The AGC control block controls the RF amplitude at the
ADC
WINDOW
DETECT
PEAK
I/D
(LOW-PASS)
FILTER
NOISE
One chip automotive CD audio device
REGISTERS
DETECT
DECAY
PEAK
HIGH-PASS
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
(DIGITAL)
FILTER
(LOW-PASS)
DETECT
DEFECT
DETECT
DECAY
Section “Peak
FILTER
NOISE
PEAK
001aab759
SAA7806
to bit detection
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