SA2420 Datasheet, PDF (6/16 Pages) NXP Semiconductors – Low voltage RF transceiver . 2.45GHz

Philips Semiconductors
Low voltage RF transceiver — 2.45 GHz
Product specification
SA2420
Table 1. Truth Table
Chip-En
TxRx-SW
0
X
1
0
1
0
1
0
1
0
1
1
1
1
LNA-SW
X
1
0
1
0
X
X
LO-SW
X
1
1
0
0
1
0
Mode
Sleep
Receive
Receive
Receive
Receive
Transmit
Transmit
LNA Gain
N/S
+14dB
-8dB
+14dB
-8dB
N/S
N/S
LO Freq. (Typ)
N/S
2.1GHz
2.1GHz
1.05GHz
1.05GHz
2.1GHz
1.05GHz
FUNCTIONAL DESCRIPTION
The SA2420 is a 2.45GHz transceiver front-end available in the
TSSOP-24 package. This integrated circuit (IC) consists of a low
noise amplifier (LNA) and up- and down-converters. The injection of
the local oscillator (LO) signal has two options: 1) direct injection of
the LO signal at approximately 2GHz, or 2) injection of an LO signal
at approximately 1GHz through an on-chip doubler. The SA2420
functions with a supply voltage range of 3 – 5 V (nominally). There
is an enable/disable switch available to power up/down the entire
chip in 1µs, typically. This transceiver has several unique features.
The LNA has two operating modes: 1) high gain mode with a gain =
+14dB; and 2) low gain mode with a gain <-10dB. The switch for
this option is internal and is controlled externally by high and low
logic to the pin. When the LNA is switched into the attenuation
mode, active matching circuitry (on-chip) is switched in (reducing the
number of off-chip components required). To reduce power
consumption when the chip is transmitting, the LNA is automatically
switched into a “sleep” mode (internally) without the use of external
circuitry.
The up and down frequency converters are single-ended at the RF
port of the mixers. The up and down converters share the same
(RF) pin and use an internal switch for transmitting (up-converting)
or receiving (down-converting) modes. The switch is controlled
externally by high and low logic states. The RF port is matched to
50Ω and has an input IP3 of +2.8dBm (mixer only). The
down-convert mixer is buffered and has open collectors at the pins
to allow for matching to common SAW filters. The up-convert mixer
has differential inputs (IF port) and single-ended output (RF port),
with an input pin to output pin gain of 17dB. The output of the
up-converter is designed for a power level = +3dBm (P_-1dB). The
mixers are fed by the two LO options.
The available LO options are: direct injection (2.1GHz at the pin) or
through an on-chip doubler. The doubler has a simple LC bandpass
filter (internal) at its output which passes the second harmonic to the
mixers. Through an internal switch (controlled externally), either LO
can be used depending on the designer’s application. If an
application requires the use of a 1.05GHz VCO, then the doubler
option would be used to double the frequency (2 × 1.05GHz =
2.1GHz) before being injected into the mixers. For a 2.1GHz VCO,
the direct option would be used. With this option, the signal passes
through an on-chip buffer and is then injected into the mixers.
1997 May 23
6