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| 型號： | IEEE 802.11 |
| 廠商： | Intersil Corporation |
| 英文描述： | () |
| 中文描述： | （） |
| 文件頁數(shù)： | 3/7頁 |
| 文件大?。?/td> | 69K |
| 代理商： | IEEE 802.11 |
2-3
On the Transmit side, data can either be DBPSK or DQPSK
modulated at 1MSPS (Mega Symbols Per Second), resulting
in a baseband quadrature signal with I and Q components.
These digital signals are output to the HFA3724 fifth order
Butterworth low pass filters, which are used to provide
shaping of the phase shift keyed (PSK) signal. The required
transmit spectral mask, at the antenna, is -30dBc at the first
side-lobe relative to the main lobe.
The signals are then quadrature modulated up to IF using
the same 2xLO used for the quadrature demodulation. The
IF output is reactively matched to FL5, the transmit IF SAW
filter. The output of FL5 is terminated in a 200
potentiometer that is used for transmit gain control.
The signal then goes to the high impedance input of the
HFA3624 upconverting mixer for conversion to the 2.4GHz
- 2.5GHz band. The mixer output is filtered with FL6, a 2
pole monolithic LC bandpass filter. This filter suppresses the
LO feedthrough from the mixer, and selects the upper
sideband. The pre-amplifier, in the HFA3624, amplifies the
selected sideband, easing the requirement for HFA3925
RFPA gain.
FL7, a two pole dielectric bandpass filter, is used to further
suppress both transmit LO leakage and the undesired
sideband. The HFA3925 RFPA amplifies the transmit signal
to approximately +20dBm. This represents a back-off from
the 1dB compression of typically 4.5dB. The transmit side-
lobe performance is approximately -32dBc to -35dBc with
this level of back-off. Allowing for a 2dB loss in the band
select filter FL1, this gives a final output power of +18dBm.
Typical radio performance is displayed in Figure 2.
Limiters vs AGCs
Generally limiters and AGCs are used to provide large gains
at the IF stage. Automatic Gain Control (AGC) circuits
maintain good signal linearity over a wide dynamic range,
even amplifying small signals buried in the noise. However,
AGCs must settle to a final value quickly. This is especially
difficult in a packetized system where AGC settling for packet
acquisition must take place in under 2
μ
s.
Limiters are nonlinear devices, eliminating amplitude
information, but work well for phase encoded modulation.
They provide the added benefit of suppressing secondary
signals and so will have up to 6dB advantage over AGCs in a
positive SNR environment.
The selection of limiters takes advantage of the modulation
scheme, positive SNR of the environment, while reducing
cost and complexity.
Receive Chain Gain Distribution Analysis
The IF stage, including the limiters, is of a differential design to
improve noise rejection and stability for these high gain stages.
The RF front end, on the other hand, is single ended to reduce
complexity. A receive chain block diagram is shown in Figure 3.
The minimum limiter 1 and 2 voltage gains are 39dB at 2.7V
and 400MHz. The radio design uses the part at a less
extreme operating point of 3.5V and 280MHz where the
minimum performance is 42dB. The limiter 1 and 2 output
limiting voltage is 200mV
P-P
into a differential 500
load.
Using 3dB loss in the limiter Bandpass Filter (BPF), the
limiter chain (LIM1, BPF, LIM2) cascaded voltage gain is
81dB, with typical performance above 90dB. With a
200mV
P-P
output, the input limiting voltage is 17.8
μ
V
P-P
or
-98dBm at 250
source impedance.
General Specifications
Targeted Standard. . . . . . . . . . . . . . . IEEE 802.11 (Draft)
Data Rate . . . . . . . . . . . . . . . . . . . . . . . . . 1Mbps DBPSK
2Mbps DQPSK
Range.. . . . . . . . . . . . . . . . . . . 400ft Indoor (Typ) (Note 1)
3700ft Outdoor (Typ) (Note 1)
Frequency Range . . . . . . . . . . . . . 2412MHz to 2484MHz
Step Size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1MHz
IF Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280MHz
IF Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17MHz
RX/TX Switching Speed . . . . . . . . . . . . . . . . . . .2
μ
s (Typ)
Operating Voltage . . . . . . . . . . . . . . . . . 4.5V
DC
- 5.5V
DC
Standby Current . . . . . . 190mA at 1
μ
s Recovery (Note 4)
70mA at 25
μ
s Recovery (Note 4)
60mA at 2ms Recovery (Note 4)
30mA at 5ms Recovery (Note 4)
Operating Temperature Range . . . . 0
o
C to 70
o
C (Note 2)
Storage Temperature Range . . . . . . . . . . .-55
o
C to 125
o
C
Mechanical . . . .Type II PC Card, with Antenna Extension
Antenna Interface . . . . . . . . . . . . . . . . . . . . . . . SMA, 50
Receive Specifications
Sensitivity. . . . .-93dBm (Typ), 1Mbps, 8E-2 FER (Note 3)
. . . . . . . . . . . . .-90dBm (Typ), 2Mbps, 8E-2 FER (Note 3)
Input Third Order Intercept Point . . . . . . . . . -17dBm (Typ)
Image Rejection . . . . . . . . . . . . . . . . . . . . . . . . 65dB (Typ)
IF Rejection . . . . . . . . . . . . . . . . . . . . . . . . . . . 80dB (Typ)
Adjacent Channel Rejection. . . . . . . . . . . . . . . 63dB (Typ)
at 25MHz Offset
Supply Current . . . . . . . . . . . . . . . . . . . . . . . .287mA (Typ)
2Mbps, 100% Duty Cycle
Transmit Specifications
Output Power . . . . . . . . . . . . . . . . . . . . . . . +18dBm (Typ)
Transmit Spectral Mask . . . . . . . . . . . . . . . . .-32dBc (Typ)
at First Side-Lobe
Supply Current . . . . . . . . . . . . . . . . . . . . . . . .488mA (Typ)
2Mbps, 100% Duty Cycle
NOTES:
1. Using M/A-COM AND-C-107 omnidirectional antenna.
2. AM79C930 limited to 0
o
C to 70
o
C.
3. FER = Frame Error Rate or Packet Error Rate.
4. Recovery times do not include MAC recovery.
FIGURE 2. TYPICAL PERFORMANCE
Application Note 9810
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