Datasheet
MAX2065
50MHz to 1000MHz High-Linearity, Serial/
Parallel-Controlled Analog/Digital VGA
______________________________________________________________________________________ 19
Detailed Description
The MAX2065 high-linearity analog/digital variable-gain
amplifier is a general-purpose, high-performance
amplifier designed to interface with 50Ω systems oper-
ating in the 50MHz to 1000MHz frequency range.
The MAX2065 integrates one digital attenuator and one
analog attenuator to provide 62dB of total gain control,
as well as a driver amplifier optimized to provide high
gain, high IP3, low noise figure, and low power consump-
tion. For applications that do not require high linearity, the
bias current of the amplifier can be adjusted by an exter-
nal resistor to further reduce power consumption.
The digital attenuator is controlled as a slave peripheral
using either the SPI-compatible interface or a parallel
bus with 31dB total adjustment range in 1dB steps. An
added feature allows “rapid-fire” gain selection
between each of the four unique steps (prepro-
grammed by the user through the SPI-compatible inter-
face). The 2-pin control allows the user to quickly
access any one of four customized attenuation states
without reprogramming the SPI bus. The analog attenu-
ator is controlled using an external voltage or through
the SPI-compatible interface using an on-chip DAC.
Because each of the three stages has its own external
RF input and RF output, this component can be config-
ured to either optimize NF (amplifier configured first),
OIP3 (amplifier last), or a compromise of NF and OIP3.
The device’s performance features include 22dB stand-
alone amplifier gain (amplifier only), 6.5dB NF at maxi-
mum gain (includes attenuator insertion loss for both
attenuators), and a high OIP3 level of +42dBm. Each of
these features makes the MAX2065 an ideal VGA for
numerous receiver and transmitter applications.
In addition, the MAX2065 operates from a single +5V
supply, or a single +3.3V supply with slightly reduced
performance, and has adjustable bias to trade current
consumption for linearity performance.
Analog and 5-Bit Digital
Attenuator Control
The MAX2065 integrates one analog attenuator and
one 5-bit digital attenuator to achieve a high level of
dynamic range. The analog attenuator has a 31dB
range and is controlled using an external voltage or
through the 3-wire serial peripheral interface (SPI) using
an on-chip 8-bit DAC. The digital attenuator has a 31dB
control range, a 1dB step size, and is programmed
through the 3-wire SPI. See the
Applications Information
section and Table 1 for attenuator programming details.
The attenuators can be used for both static and dynam-
ic power control.
Driver Amplifier
The MAX2065 includes a high-performance driver with
a fixed gain of 22dB. The driver amplifier circuit is opti-
mized for high linearity for the 50MHz to 1000MHz fre-
quency range.
Applications Information
SPI Interface and Attenuator Settings
The digital attenuator is programmed through the 3-wire
SPI/MICROWIRE™-compatible serial interface using
5-bit words. Twenty-eight bits of data are shifted in MSB
first and is framed by CS. When CS is low, the clock is
active and data is shifted on the rising edge of the
clock. When CS transitions high, the data is latched
and the attenuator setting changes (Figure 1). See
Table 2 for details on the SPI data format.
Table 1. Control Logic
VDAC_EN SER/PAR VR EF _ SEL EC T
ANALOG
ATTENUATOR
DIGITAL
ATTENUATOR
D/A CONVERTER
00X
Controlled by external
control voltage
Parallel controlled Disabled
101
Controlled by on-chip
DAC
Parallel controlled
Enabled (DAC uses on-
chip voltage reference)
01X
Controlled by external
control voltage
SPI controlled Disabled
110
Controlled by on-chip
DAC
SPI controlled
Enabled (DAC uses
external voltage
reference)
X = Don’t care.
MICROWIRE is a trademark of National Semiconductor Corp.