參數(shù)資料
型號(hào)： UAA1570HL
廠商： NXP SEMICONDUCTORS
元件分類： 通信及網(wǎng)絡(luò)
英文描述： Global Positioning System (GPS)baseband processor(通用定位系統(tǒng)基帶處理器)
中文描述： SPECIALTY TELECOM CIRCUIT, PQFP48
封裝： PLASTIC, SOT-313, LQFP-48
文件頁(yè)數(shù)： 24/76頁(yè)
文件大?。?/td> 890K
代理商： UAA1570HL
1999 May 10
24
Philips Semiconductors
Product specification
Global Positioning System (GPS) front-end
receiver circuit
UAA1570HL
7.4
VCO
The VCO consists of a single transistor in common
collector configuration with internal positive feedback
realized by capacitors connected from emitter to ground
and emitter to base. Together with the external
resonator/inductor, this is a typical Colpitts circuit. With the
transistor’s base connected to pin 10 (TANK), the internal
circuit arrangement produces a large negative input
impedance at this pin.
At V
CCA
= 3 V and T
amb
= 27
°
C the oscillator transistor is
initially biased with approximately 1.5 mA of start-up
current. This value is relatively constant varying from
approximately 1.56 mA at T
amb
= +120
°
C to 1.4 mA at
T
amb
=
55
°
C. During operation, the average currents are
higher due to the large amplitudes involved leading to
rectification and bias point shifting.
The VCO operates as a negative impedance oscillator with
a suitable external inductive resonator.
Series or parallel resonators can be used, while tuning is
achieved by an external varactor diode.
VCO gain as well as the out-of-loop bandwidth phase
noise are dependent on the choice of external elements
used here. Consequently, they should be selected with
great care; their quality factor is especially important and
should be as high as possible.
Finally, the VCO is followed by a differential buffer stage
with emitter follower inputs splitting the signal to the divider
and LO driver stage path to increase isolation between
mixer and synthesizer and their wanted or unwanted
signals.
This first buffer stage is followed by two other specialized
buffer amplifier stages in the individual signal paths
bringing the signal to the required levels for driving a mixer
or a divider.
Fig.15 Simulated VCO small signal negative resistance (top diagram) and capacitance (below), without strays.
(1) T
amb
=
55
°
C.
(2) T
amb
= +27
°
C.
(3) T
amb
= +120
°
C.
handbook, full pagewidth
3
0
0.5
1
1.5
2
2
4
0
0
100
2.5
MHB278
f (GHz)
R
(
)
C
(pF)
(2)
(3)
(1)
(2)
(3)
(1)
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