Datasheet

MAX2831/MAX2832
2.4GHz to 2.5GHz 802.11g/b
RF Transceivers with Integrated PA
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Receiver I/Q Baseband Outputs
The differential outputs (RXBBI+, RXBBI-, RXBBQ+,
RXBBQ-) of the baseband amplifiers have a differential
output impedance of ~300Ω, and are capable of dri-
ving differential loads up to 10kΩ || 10pF. The outputs
are internally biased to a common-mode voltage of
1.1V and are intended to be DC-coupled to the in-
phase (I) and quadrature (Q) analog-to-digital data
converter inputs of the accompanying baseband IC.
Additionally, the common-mode output voltage can be
adjusted from 1.1V to 1.4V through programming bits
D11:D10 in Register 15 (A3:A0 = 1111).
Received Signal-Strength Indicator (RSSI)
The RSSI output (pin 16) can be programmed to multi-
plex an analog output voltage proportional to the
received signal strength, the PA output power
(MAX2831), or the die temperature. Set bits D9:D8 = 00
in Register 8 (A3:A0 = 1000) to enable the RSSI output
in receive mode (off in transmit mode). Set bit D10 = 1
to enables the RSSI output when RXHP = 1, and dis-
able the RSSI output when RXHP = 0. Set bit D10 = 0 to
enable the RSSI output independent of RXHP. See
Table 7 for a summary of the RSSI output versus regis-
ter programming and RXHP.
The received signal strength indicator provides an ana-
log voltage proportional to the log of the sum of the
squares of the I and Q channels, measured after the
receive baseband filters and before the variable-gain
amplifiers. The RSSI analog output voltage is propor-
tional to the RF input signal level and LNA gain state
over a 60dB range, and is not dependent upon VGA
gain. See the graph RX RSSI Output vs. Input Power in
the Typical Operating Characteristics for further details.
Transmitter
The transmitter integrates baseband lowpass filters,
direct-upconversion mixers, a VGA, a PA driver, and a lin-
ear RF PA with a power detector (MAX2831). A logic-high
on the RXTX input (pin 48) and a logic-high on the SHDN
input (pin 12) enable the transmitter.
Transmitter I/Q Baseband Inputs
The differential analog inputs of the transmitter baseband
amplifier I/Q inputs (TXBBI+, TXBBI-, TXBBQ+, TXBBQ-)
have a differential impedance of 20kΩ || 1pF. The inputs
require an input common-mode voltage of 0.9V to 1.3V,
which is provided by the DC-coupled I and Q DAC out-
puts of the accompanying baseband IC.
Transmitter Baseband Lowpass Filtering
The transmitter integrates lowpass filters that can be
tuned to -3dB corner frequencies of 8MHz (11b),
11MHz (11g), 16.5MHz (turbo 1 mode), and 22.5MHz
(turbo 2 mode) through programming bits D1:D0 in
Register 8 (A3:A0 = 1000) and bit D5:D3 in Register 7
(A3:A0 = 0111). The -3dB corner-frequency is tightly con-
trolled on-chip and does not require user adjustment.
Additionally, provisions are made to fine tune the -3dB cor-
ner frequency through bits D5:D3 in the Filter
Programming register (A3:A0 = 0111). See Tables 8 and 9.
Table 7. RSSI Pin Truth Table
Table 8. Transmitter LPF Coarse -3dB
Corner Frequency Settings in Register
(A3:A0 = 1000)
BITS (D1:D0)
-3dB CORNER
FREQUENCY (MHz)
MODE
00 8 11b
01 11 11g
10 16.5 Turbo 1
11 22.5 Turbo 2
Table 9. Transmitter LPF Fine -3dB
Corner Frequency Adjustment in
Register (A3:A0 = 0111)
BITS (D5:D3)
% ADJUSTMENT RELATIVE TO
COARSE SETTING
000 90
001 95
010 100
011 105
100 110 (11g)
101 115
101–111 Not used
INPUT CONDITIONS
A3:A0 = 1000,
D9:D8
A3:A0 = 1000,
D10
RXHP
RSSI OUTPUT
X 0 0 No signal
00 0 1 RSSI
01 0 1
Temperature
sensor
10 0 1
Power detector
(MAX2831)
00 1 X RSSI
01 1 X
Temperature
sensor
10 1 X
Power detector
(MAX2831)
X = Don’t care.