SA58646 Datasheet, PDF (12/42 Pages) NXP Semiconductors – UHF 900 MHz transceiver IC

NXP Semiconductors
SA58646
UHF 900 MHz transceiver IC
7.5 RX baseband
This section covers the RX audio path from pins RXAI to EARO. The RXAI input signal is
AC-coupled. The microcontroller sets the value of the RX gain with 32 linear steps of
0.5 dB. The RX baseband has a mute and an expander with the characteristics shown in
Figure 7. The audio level is programmable over a dynamic range of 31 dB by the RX gain
control. The expander slope multiplies the RX gain step by 2 to achieve 1 dB steps on the
earpiece output. Noise coming from, and within, the RX baseband can be shaped thanks
to a ‘noise control’ programmability. It provides the possibility to attenuate the expander
gain at low input level. Figure 7 provides some information about the noise shaper
function. The earpiece amplifier is an inverting rail-to-rail operational amplifier. The
non-inverting input is connected to the internal VB reference voltage. Software volume
control on the earpiece amplifier is done by integrated switched feedback resistances.
Volume control tuning range is 14 dB. Hardware volume control is done by externally
switching the earpiece feedback resistance.
RXAI
RX gain
MUTE
RX_GAIN
[4:0]
RX_MU
EXPANDER
EXP[1:0]
ECAP
EARP_VOL
[1:0]
earpiece
amplifier
VB
EARP
Fig 6. RX baseband part
EARI
EARO
001aaf621
SA58646_1
Product data sheet
V_EARO
(dBV)
0
−10
EXPDR_out = −7 dBV
(typical at THD < 4 %)
−20
y = 2x + 20
−30
−40
−50
noise shaping
−60
−45 −40
−30
−20
−10
0
10
V_RXAI (dBV)
001aaf622
RX gain adjustment at 0 dB; volume earpiece at 0 dB; no external resistance.
Fig 7. Expander characteristic
Rev. 01 — 8 February 2007
© NXP B.V. 2007. All rights reserved.
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