SAA8200HL Datasheet, PDF (35/71 Pages) NXP Semiconductors – Ensation Base integrated wireless audio baseband

Philips Semiconductors
SAA8200HL
Ensation Base integrated wireless audio baseband
7.19.1.2 LNA
LNA, a Low Noise microphone Amplifier with nominal gain of 30 dB.
7.19.1.3 PGA
The input signal is amplified with a gain set by control bits CTRL[3:0]. The resulting signal
will be available at V_out. If control bit CTRL3 = 1 the gain is set to 24 dB independent of the
other bits. If CTRL3 = 0 the gain is set for other (lower) settings. The PGA is based on an
inverting amplifier architecture. The feedback resistance exists of a resistor string. By
switching between different resistors with the use of a 4-bit digital decoder the gain of the
amplifier can be modified. The gain can be set in steps of 3 dB from 0 dB up to 24 dB (see
Table 15). The PGA is designed to handle a nominal 1 V (RMS) input level. A systematic
gain of −1.94 dB is added to accommodate the 800 mV (RMS) input level of a
single-to-differential converter that is normally connected to the PGA output. The
power-down signal is controlled by the digital core of the SAA8200HL.
Table 15: PGA gain settings
CTRL3
CTRL2
0
0
0
0
0
0
0
0
0
1
0
1
0
1
0
1
1
X
CTRL1
0
0
1
1
0
0
1
1
X
CTRL0
0
1
0
1
0
1
0
1
X
Gain
0 dB
3 dB
6 dB
9 dB
12 dB
15 dB
18 dB
21 dB
24 dB
7.19.1.4 Applications with 2 V (RMS) input
For the Line-in mode it is preferable to have 0 dB and 6 dB gain setting in order to be able
to apply both 1 V (RMS) and 2 V (RMS) (using series resistance). For this purpose a PGA
is used which has 0 dB to 24 dB gain with 3 dB steps.
input signal
external
resistor
12 kΩ
12 kΩ
PGA
001aab456
Input signal is 2 V (RMS); V_DD = 3 V.
Fig 7. ADC front-end with PGA (line-in input)
In applications in which a 2 V (RMS) input signal is used, a 12 kΩ resistor must be used in
series with the input of the ADC. This forms a voltage divider together with the internal
ADC resistor and ensures that only 1 V (RMS) maximum is input to the SAA8200HL.
Using this application for a 2 V (RMS) input signal, the switch must be set to 0 dB. When a
1 V (RMS) input signal is input to the ADC in the same application, the gain switch must
be set to 6 dB.
SAA8200HL_2
Preliminary data sheet
Rev. 02 — 17 October 2005
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
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