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參數(shù)資料
| 型號(hào)： | AD6190ARS |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 無繩電話/電話 |
| 英文描述： | 900 MHz RF Transceiver |
| 中文描述： | TELECOM, CORDLESS, BASEBAND CIRCUIT, PDSO28 |
| 封裝： | SSOP-28 |
| 文件頁數(shù)： | 7/8頁 |
| 文件大?。?/td> | 150K |
| 代理商： | AD6190ARS |
AD6190
–7–
REV. 0
T ransmit Signal Path
T he AD6190 transmit chain is designed to accept an input
signal generated by the Z87L00 device. T he Z87L00 provides
a digitally-generated FSK signal at 2.508 MHz, sampled at
8.192 MSPS. T his sampling process produces a signal with com-
ponents at 2.508 MHz, 5.684 MHz, 10.7 MHz, 16.386 MHz,
and other higher-order image products at frequencies of (N
×
8.192 MHz
±
2.508) MHz. T his signal is filtered to select the
10.7 MHz image, which is used as the transmit IF signal for the
AD6190.
An image-reject transmit up-converts the 10.7 MHz IF signal to
the 902 MHz–928 MHz RF band, with image and spurious
outputs typically 45 dB below the desired signal, and LO leak-
age typically –33 dBc.
T he on-chip driver can provide at least 1 mW (0 dBm) into a
50
load. However, when driving an external Power Amplifier
(PA) with a gain of 15 dB or more, we recommend a nominal
driver output power no higher than –3 dBm (137 mV p-p T X IF
input level) to avoid spurious PA output products in excess of
FCC allowances. T he RFOUT pin is normally connected through
an 8.2 nH dc feed inductor, and ac-coupled to the power amplifier.
TXOUT
2.2pF
8.2nH
TO 50
V
LOAD
AD6190
+3.3V
Figure 10. TXOUT Matching Circuit
Frequency Control
T he AD6190 includes an on-chip voltage controlled oscillator
for LO generation. An external varactor-tuned tank circuit con-
trols the frequency. T his VCO operates at twice the required
LO frequency for several reasons.
First, it is a simple matter to generate the I and Q LO compo-
nents needed for the image-reject mixers by starting with a LO
at twice the desired frequency. T he divide-by-two process can
easily provide coarse quadrature signals. Any remaining phase
error is further reduced by an on-chip connection network.
Second, by keeping the oscillator operating at a frequency far
removed from the RF carrier frequency, parasitic feedback from
either the transmit signal or strong received signals is minimized.
T his reduces VCO “pulling” effects.
A typical series resonant VCO tank circuit is shown in Figure
11. T he oscillator actually operates at twice the required LO
frequency band. T he tank inductors (L1, L2) may be imple-
mented as printed traces on the PC board or as lumped circuit chip
components. T he printed lines are implemented in nonmicrostrip
to produce higher Q. At least two foil layers should be removed
immediately under the tank area. A suitable tank structure can
be formed from two parallel lines, each approximately 7 mm
long by 0.3 mm wide, continuing out from the device pads. In
other words, the Pin 5 and Pin 7 pads are simply extended to
form L1 and L2. Equivalent Hi-Q chip inductors in the 2.2 nH
to 4.7 nH range may be substituted.
T he single tuning varactor, D1, (e.g., Alpha Industries SMV-
1233-011) and a fixed capacitor C1 (or a common anode dual
diode) are located on the ends of the lines. Note that this is a
positive supply (VREG) referenced “pump-down” tank, mean-
ing that as the T UNE voltage is increased toward VREG, the
frequency goes down. T he loop filter return should also be
referenced to VREG (not ground) in order to minimize com-
mon-mode noise pickup and frequency pushing. T he designer is
cautioned to develop a tank with only as much kVCO as re-
quired to allow easy coverage of the band with respect to com-
ponent tolerance and production issues, in order to minimize
phase noise and frequency pulling.
TANK–
100nF
C1
15nH
39
V
AD6190
GND
TANK+
VCLO
82pF
LOOP FILTER
RETURN
(FROM REGULATOR
PASS TRANSISTOR)
15nH
15nH
L2
L1
D1
VTUNE (FROM
LOOP FILTER)
39
V
Figure 11. Typical VCO Tank Circuit
An on-chip dual-modulus (64/65) prescaler allows the frequency
control to be done with a low-cost low-frequency PLL synthe-
sizer chip, such as the Fujitsu MB87006A, Siemens PMB2307,
or similar.
T he prescaler output should be connected to ground through a
2.2 k
pull-down resistor. T he output signal (typically 1 V p-p)
is sufficient to drive most low cost PL L s, and is usually ac-
coupled through a 1 nF capacitor to the PLL input.
Layout, Grounding and Decoupling
T he AD6190 is a complex device with high bandwidth and high
gain on-chip. Proper layout, grounding and decoupling, tech-
niques are essential to realizing the full performance of the sys-
tem. Each of the power supply pins should be decoupled to
ground at the chip using a 82 pF chip capacitor in parallel with
a 10 nF chip capacitor. T he VCCIF pin requires a 10
series
resistor in addition to the 82 pF shunt capacitor.
Voltage Regulator
T he AD6190 includes an on-chip voltage regulator to stabilize
the supply voltage for the local oscillator, isolating it from any
variations or noise on the main power supply voltage in the
system. T his regulator is nominally set for 2.75 V output. An
external PNP pass transistor provides the needed output current
for the VCO.
T his regulator is intended to stabilize the voltage for the LO
only, and should not be used for other circuitry. VBAT T may
be connected to a 3.3 V dc preregulator or to the precondi-
tioned three-cell battery system.
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