Datasheet

MAX2371/MAX2373
LNAs with Step Attenuator and VGA
8 _______________________________________________________________________________________
Detailed Description
The MAX2371/MAX2373 are single-channel, single-
ended, low-noise amplifiers with two gain modes and
continuous automatic gain control (AGC) in both
modes. The devices are intended as low-noise gain
stages for direct conversion receivers (DCR) or very
low IF (VLIF) receivers. These devices provide high
gain-control dynamic range (typ 60dB) at RF with
excellent noise and reverse isolation characteristics.
Vary the resistor at pin RSET and the inductor at LNA_E
to meet a wide range of gain and linearity require-
ments. The ICs can be dynamically configured through
pins LNA_I and RF_ATTN. When LNA_I is connected to
V
CC
, the LNA is in high-current mode, nominally config-
ured for maximum gain and low noise figure of the
amplifier. If the LNA_I pin is grounded, the current of
the LNA is reduced, and the associated gain, input IP3,
and noise figure are degraded. The devices have two
gain modes configured by the RF_ATTN pin. Set
RF_ATTN high for low-gain mode; set RF_ATTN low for
high-gain mode. The gain step between these two gain
modes typically is 20dB.
Table 4. MAX2373 Typical Noise Parameters
(V
CC
= 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, P
IN
= -30dBm, T
A
= +25°C, data from design simulation.)
FREQUENCY (MHz) NF
MIN
(dB) ⎜Γ
OPT
⎟∠ Γ
OPT
R
N
(Ω)
850 1.06 0.35 60.5 10.02
870 1.08 0.35 61.8 9.98
890 1.10 0.34 63.3 9.94
910 1.11 0.34 64.7 9.90
930 1.13 0.33 66.2 9.86
950 1.15 0.33 67.7 9.82
Pin Description
PIN NAME FUNCTION
1 LNA_IN RF Input. Requires DC-blocking capacitor and external matching network.
2 LNA_E LNA Emitter. Connect to GND with an inductor. See inductor value in Table 5.
3 RX_EN LNA Control. Set RX_EN high to enable LNA; set RX_EN low to disable LNA.
4
RF_ATTN
Attenuator Control. Set RF_ATTN high for low-gain mode; set RF_ATTN low for high-gain mode.
5 AGC
AGC Input Voltage. Set AGC to V
CC
/2 for maximum gain. Set AGC to V
CC
- 200mV for minimum gain. If
left unconnected, the LNA will operate at maximum gain and optimum noise figure.
6 LNA_I
LNA Nominal Bias-Current Setting. Set LNA_I high for high-current mode. Set LNA_I low for low-current
mode. If left unconnected, the default state of the LNA is high-current mode.
7
LNA_OUT
RF Output Pin. Requires a pullup inductor to LNA_V
CC
and external matching network.
8
LNA_V
CC
Supply Voltage for the AGC Amplifier
9
AGC_BYP
AGC Bypass. Connect a capacitor to ground. The value of the capacitor is a compromise of AGC
response time and blocker frequency offset.
10 RSET
External pin for precision resistor to ground to set reference bias current for IC; typical bias current is
50µA to 100µA.
11 RF_V
CC
Supply Voltage for the LNA. Bypass with a capacitor to GND as close to the pin as possible. Do NOT
connect any tuned circuits to this supply pin.
12 GND Ground
EP
Exposed
Pad
Internally connected to GND. Connect to a large ground plane to maximize thermal performance.
Do not use as the sole ground connection point.
BAND
L SERIES VALUE
(nH)
LNA TYPE
150MHz (VHF) 33 Low Band
450MHz (UHF) 10 Low Band
450MHz (UHF) 2.7 High Band
800MHz 2.5 High Band
1GHz 1.8 High Band
Table 5. Inductor Selection