参数资料
型号: MRFIC1502
厂商: MOTOROLA INC
元件分类: 衰减器
英文描述: 1.575GHz GPS Downconverter(1.575GHz GPS下转换器)
中文描述: RF/MICROWAVE DOWN CONVERTER
封装: PLASTIC, LQFP-48
文件页数: 5/7页
文件大小: 163K
代理商: MRFIC1502
5
MRFIC1502
MOTOROLA RF DEVICE DATA
circuit, the VCO is centered at 1527.7 MHz, and the gain of
the VCO is approximately 20 MHz/Volt.
The above performance is heavily dependent on the ca-
pacitive structure that is used as the emitter bypass on pin 6.
The total capacitance should be approximately 1.0 pF; that
can be achieved using either a discrete element or a micro-
strip open circuited stub. The evaluation circuit shown uses a
0.4 pF capacitor.
Phase–locked Loop Design
The VCO signal at 1527.68 MHz is divided by 40 to get the
second LO frequency of 38.19 MHz. In addition to providing
the LO to the second mixer, the 38 MHz signal is output
through a translator and is used as the sampling clock for the
digital correlator and decimator circuits. There is an addition-
al divide by two so the signal used by the phase detector is at
19.096 MHz. The reference input to the phase detector (pin 18)
has an input sensitivity of 400 mVpp minimum and 2.5 Vpp
maximum.
The loop filter design is the standard op–amp loop filter,
resulting in a type 2 second order loop. The layout of the
discrete components around the loop filter and VCO is very
critical to the performance of the phase–locked loop. Care
should be taken in routing the VCO control voltage line from
the output of the loop filter to the varactor diode.
The output of the divide by 40 is buffered by a clock trans-
lator that converts the low level sine wave into a TTL level
square wave. The loading on the buffer is high so the peak
currents can reach as high as 50 mA with the maximum load
of 1.0 k
in parallel with 40 pF on the output. Therefore, the
translator has a dedicated VCC supply, pin 28, which requires
external bypassing and isolation. The recommended bypas-
sing uses two capacitors in parallel, a 47 pF and a 0.01
μ
F
capacitor.
Conclusion
The MRFIC1502 offers a highly integrated downconverter
solution for GPS receivers. For more detailed applications in-
formation on GPS system design refer to application note
AN1610, “Using Motorola’s MRFIC1502 in Global Positioning
System Receivers.”
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