ARA2017_12 Datasheet, PDF (14/17 Pages) ANADIGICS, Inc – Programmable Gain Amplifier

ARA2017
APPLICATION INFORMATION
Transmit Enable / Disable
The ARA2017 can be switched on (TX enable) and off
(TX disable) via an asynchronous input TX_EN (pin
13). A logic high will turn the amplifier on. The gain
and current settings are retained during Tx disable
and do not need to be reloaded.
Gain/Attenuator Setting
The gain of the ARA2017 can be controlled via the
3-wire bus. Data bits D2 through D6 set the gain/
attenuator level, with 00000 being the min gain setting,
and 11111 being the max gain setting. A new gain/
attenuator setting can be loaded while the PGA is on
(TX enable), but will not take effect until TX_EN has
been cycled off /on.
Output Stage Current Setting
The ARA2017 consists of 2 gain stages. The input
stage operates at a constant fixed current when TX
is enabled. The current in the output stage can be
controlled via the 3-wire bus. Data bits D7 – D9 set
the current. 111 will set the output stage to maximum
current for maximum linearity. The current can be
lowered for improved efficiency at lower output
power levels, or lower linearity requirements. 000 will
turn both stages off, the same as TX disable. A new
current setting can be loaded while the PGA is on (TX
Enable), but will not take effect until TX_EN has been
cycled off /on.
Output Transformer
Matching the balanced output of the ARA2017 to a
single-ended 75  load is accomplished using a 1:1
turns ratio transformer. In addition to the balanced to
single-ended conversion, this transformer provides the
bias to the output amplifier stage via the center tap.
The transformer also cancels even mode distortion
products and common mode signals, such as the
voltage transients that occur while enabling and
disabling the amplifiers. As a result, care must be
taken when selecting the transformer to be used at
the output. It must be capable of handling the RF and
DC power requirements without saturating the core,
and it must have adequate isolation and good phase
and amplitude balance. It also must operate over
the desired frequency and temperature range for the
intended application.
14
DATA SHEET - Rev 2.1
11/2012