Datasheet
MAX2831/MAX2832
2.4GHz to 2.5GHz 802.11g/b
RF Transceivers with Integrated PA
22 ______________________________________________________________________________________
Baseband Variable-Gain Amplifier
The receiver baseband variable-gain amplifiers provide
62dB of gain control range programmable in 2dB steps.
The VGA gain can be serially programmed through the
SPI interface by setting bits D4:D0 in Register 11 (A3:A0
= 1011) or programmed in parallel through the digital
logic gain-control pins, B5 (pin 14), B4 (pin 34), B3 (pin
8), B2 (pin 11), and B1 (pin 23). Set bit D12 = 1 in
Register 8 (A3:A0 = 1000) to enable serial programming
through the serial interface or set bit D12 = 0 to enable
parallel programming through the external logic pins.
See Table 2 for the gain-step value and Table 3 for
baseband VGA gain-control settings.
Receiver Baseband Lowpass Filter
The receiver integrates lowpass filters that provide an
upper -3dB corner frequency of 8.5MHz (nominal mode)
with 50dB of attenuation at 20MHz, and 45ns of group
delay ripple in the passband (10kHz to 8.5MHz). The
upper -3dB corner frequency is tightly controlled on-chip
and does not require user adjustment. However, provi-
sions are made to allow fine tuning of the upper -3dB cor-
ner frequency. In addition, coarse frequency tuning
allows the -3dB corner frequency to be set to 7.5MHz
(11b mode), 8.5MHz (11g mode), 15MHz (turbo 1 mode),
and 18MHz (turbo 2 mode) by programming bits D1:D0
in Register 8 (A3:A0 = 1000). See Table 4. The coarse
corner frequency can be fine-tuned approximately ±10%
in 5% steps by programming bits D2:D0 in Register 7
(A3:A0 = 0111). See Table 5 for receiver LPF fine -3dB
corner frequency adjustment.
Baseband Highpass Filter
and DC Offset Correction
The receiver implements programmable AC and near-
DC coupling of I/Q baseband signals. Temporary AC-
coupling is used to quickly remove LO leakage and
other DC offsets that could saturate the receiver out-
puts. When DC offsets have settled, near DC-coupling
is enabled to avoid attenuation of the received signal.
AC-coupling is set (-3dB highpass corner frequency of
600kHz) when a logic-high is applied to RXHP (pin 40).
Near DC-coupling is set (-3dB highpass corner fre-
quency of 100Hz nominal) when a logic-low is applied
to RXHP. Bits D13:D12 in Register 7 (A3:A0 = 0111)
allow the near DC-coupling -3B highpass corner fre-
quency to be set to 100Hz (D13:D12 = 00), 4kHz
(D13:D12 = X1), or 30kHz (D13:D12 = 10). See Table 6.
Table 2. Receiver Baseband VGA Gain-
Step Value (Pins B5:B1 or Register D4:D0,
A3:A0 = 1011)
Table 3. Baseband VGA Gain-Control
Settings in Receiver Gain-Control Register
(Pin B5:B1 or Register D4:D0, A3:A0 = 1011)
Table 4. Receiver LPF Coarse -3dB
Corner Frequency Settings in Register
(A3:A0 = 1000)
Table 5. Receiver LPF Fine -3dB Corner
Frequency Adjustment in Register
(A3:A0 = 0111)
PIN/BIT GAIN STEP (dB)
B1/D0 2
B2/D1 4
B3/D2 8
B4/D3 16
B5/D4 32
BITS (D2:D0)
% ADJUSTMENT RELATIVE TO
COARSE SETTING
000 90
001 95
010 100
011 105
100 110
B5:B1 OR D4:D0 GAIN
11111 Max
11110 Max - 2dB
11101 Max - 4dB
::
00000 Min
BITS (D1:D0)
-3dB CORNER
FREQUENCY (MHz)
MODE
00 7.5 11b
01 8.5 11g
10 15 Turbo 1
11 18 Turbo 2
Table 6. Receiver Highpass Filter -3dB
Corner Frequency Programming
RXHP
A3:A0 = 0111,
D13:D12
-3dB HIGHPASS CORNER
FREQUENCY (Hz)
1 XX 600k
0 00 100 (recommended)
0X1 4k
0 10 30k
X = Don’t care.