SA1620 Datasheet, PDF (14/26 Pages) NXP Semiconductors – Low voltage GSM front-end transceiver

Philips Semiconductors
Low voltage GSM front-end transceiver
Product specification
SA1620
APPLICATION CIRCUIT
LNA
Impedance Match: Intrinsic return losses at the input and output
ports are 7dB and 11dB, respectively. However, since long and
narrow traces are always needed to fan out the pins, the user can
adjust the traces’ dimensions so that only one shunt capacitor at the
input is required to achieve excellent impedance match for both
ports. If the user wants to skip the input matching network for
simplicity, then roughly 0.7dB gain would be lost, although it benefits
the system IP3.
Noise Match: The LNA1 and LNA2 can achieve 1.9dB and 2.0dB
noise figure, respectively, when S11 = –11dB. Further improvement
in S₁₁ will slightly decrease NF and increase S₂₁.
Gain Control: The LNA1 can be switched to the attenuation mode,
while LNA2 has three attenuation modes to choose from. When
gain and loss modes from two LNAs are combined, there will be a
total dynamic range of 59dB in the RF block; 3.0V operation is
preferred to achieve better IP3 for both LNA1 and LNA2.
Temperature Compensation: Both LNAs have a built–in temperature
compensation scheme to reduce the gain drift rate to 0.003dB/°C
from –40°C to +85°C.
Supply Voltage Compensation: Unique circuitry provides gain
stabilization over wide supply voltage range. The gain changes no
more than 0.5dB when V_CC increases from 2.7V to 5.5V.
Mixer
Mixer Input Match: The mixer is configured for best gain, noise
figure and spurious response. The user must supply an external,
patented resonant balun to provide the differential drive as well as
the impedance match (embedded in). Because the mixer consists
of two single–balance mixers, whose inputs are connected in
parallel instead of in series, the differential and common–mode
impedances are equal.
Output Match: The mixer output circuit also features an external,
patented resonant balun to optimize the conversion gain and noise
figure. The principal IF operating frequency is 400 MHz.
LO Drive: The internal buffer only requires –15dBm from an external
source. Furthermore, the transmitter incorporates an integrated
SSB upconverter that consists of narrowband phase shifters at
1300MHz (LO side) and 400MHz (IF side), so the LO frequency is
recommended to be the receiver band plus 400MHz. Additionally,
the LO leakage at the input of LNA1 is extremely low, which can
greatly alleviate the LO re–radiation problem.
Outband Blocking: For optimum performance, passive R/C network
is added at each input of the mixer. The resistors degenerate the
noise conversion gain, while the capacitors preserve the gain and
noise figure at RF frequencies.
Noise Figure and IP3: The resonant balun is superior to the
conventional balun in terms of insertion loss, size and cost. As a
result, the user can expect excellent SSB noise figure and gain
which is 10dB and 8.5dB, respectively, at 400MHz IF. And the
associated input IP3 is 2dBm typically. In the meantime, due to the
internal LO buffer, the noise figure and IP3 are not sensitive to the
LO levels. As discussed in the LNA Impedance Match session, a
better system IP3 can be achieved (if necessary) through LNAs’
gain reduction.
Transmitter
The resonant balun is applied again to maximize the gain and output
power, for a given bias current. Typical output power is 8.5dBm
when the input level exceeds –25dBm.
LO Input
The LO input is used in Tx- and in Rx-mode.
Only one synthesizer PLL is necessary to supply the LO input with
different frequencies in Tx and Rx timeslots.
The LO input buffer should only be set in power-down mode
together with the PLL. As further buffering is included on chip there
will be no influence on the PLL in active mode when the SA1620 Rx-
or Tx-path is power On or Off. Current consumption can thus be
saved by powering on the Rx- and Tx-circuitry just before it is
required, without disruption of the LO circuitry. LO input pins LO IN
and LO INX may be used single-ended or symmetrically.
Table 5. GSM/DSC1800 Frequency Specification
(GSM 05.05, Version 4.2.0, April 1992) Mobile Stations Frequency
Bands
GSM
EGSM
DCS1800
Unit
Tx 890 to 915 880.2 to 915 1710 to 1785 MHz
Rx 935 to 960 925.2 to 960 1805 to 1880 MHz
1997 May 22
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