參數(shù)資料
型號(hào): GS1522
廠商: Electronic Theatre Controls, Inc.
英文描述: HDTV Serial Digital Serializer
中文描述: 高清晰度電視串行數(shù)字串行
文件頁數(shù): 16/20頁
文件大?。?/td> 414K
代理商: GS1522
GENNUM CORPORATION
522 - 26 - 00
16
G
18. RETURN LOSS
In the application where the GS1522 directly drives a cable,
it is possible to achieve an output return loss (ORL) of about
17dB to 1.485GHz. Care should be taken with the PCB
layout. It is suggested to use the EB1522 as a reference
layout. The use of very small
0608
surface mount
components and short distances between the components
will help in designing high frequency circuits. Openings in
the ground plane helps reduce PCB parasitic capacitance.
For best matching, a 12nH inductor in parallel with a 75
resistor and a 1.5pF capacitor matches the 75
cable
impedance. The inductor and resistor cancel the parasitic
capacitance while the capacitor cancels the inductive effect
of the bond wire. In order to verify the performance of any
layout, a return loss measurement should be done by
shorting the inductor with a piece of wire, without the
GS1522 installed.
Unless the artwork is an exact copy of the recommended
layout, every design should be verified for output return
loss. Changes in the layout should be tweaked until a return
loss of 25dB is attained while the GS1522 is not mounted
and L1 is shorted. Once the device is mounted, different
inductors should be used to match the parasitic
capacitance of the IC. When the right inductor is used,
maximum return loss between 5MHz to 800MHz is
achievable. Then the shunt capacitor between of 0.5pF to
1.5pF should be tried to increase the return loss between
800MHz and 1.5GHz. The larger inductor causes slower
rise/fall time. The larger shunt capacitor causes a kink in the
output waveform. Thus, the waveform must be verified to
meet SMPTE 292M specifications.
Since there are two levels at the output, depending upon
the output state (logic high or low), measurement should be
taken by latching the outputs in both states. Since the
actual output node voltages are different when a stream of
data passing as compared to the static situation created to
measure return loss, an interpolation is necessary. See the
GS1508 Preliminary Data Sheet for more information
Fig. 26 Compensated Output Return Loss at Logic HIGH
Fig. 27 Compensated Output Return Loss at Logic LOW
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