參數(shù)資料
型號(hào)： WE904
廠商： Electronic Theatre Controls, Inc.
英文描述： 0.1 - 1GHx Single Chip FM Transceiver
中文描述： 0.1 - 1GHx單芯片F(xiàn)M收發(fā)器
文件頁(yè)數(shù)： 18/39頁(yè)
文件大?。?/td> 623K
代理商： WE904
Winceiver WE904/WE905
WiNEDGE & WiRELESS
0.1 - 1GHz Single Chip FM Transceiver
2003 WiNEDGE & WiRELESS PTE LTD
Page 25
Rev Date: 2003 May 27
SWITCHING AFC ON AND OFF DURING OPERATION
When AFC is switched off, AFC output voltage will drop to 0V. The varactor capacitance will become
maximum and pull the reference frequency to lowest point of the AFC correction range.
Therefore, if the application requires switching AFC off during operation, the resistor network R9 –
R11 is required to provide a DC1.2V at the varactor. However, if AFC is always on during operation,
this resistor network can be omitted.
CRYSTAL TUNING WITH AFC
While tuning trimmer capacitor (TC1) to correct crystal error, it is necessary to fix the AFC voltage at
mid value (1.2V)
This can be done by:
1.
turning AFC off if the resistor network R9 – R11 is in placed. Adjust TC1 until the Tx
frequency is the same as the Tx Frequency Register.
2.
connecting the Rx to a reference signal generator which is set to the receiving frequency of
the Rx Frequency Register. Turn AFC on. Adjust TC1 until AFC voltage is about 1.2V.
WORKING CONDITIONS FOR AFC
In a pair of transceivers, AFC is only required in one transceiver; although it is fine to have AFC on
both transceivers.
In order for AFC to work properly, the receiving frequency must fall within the bandwidth of the
receiver; and the frequency offset between receiving frequency and Rx LO must not be larger than
what the AFC correction range can provide.
In data communication (FSK modulation) with low baud rate or without using non-return-to-zero
technique, AFC may treat FSK deviation as frequency offset and “correct” it. In such situation, AFC
should not be used.
AFC NOISE
Although AFC removes the beat tone, it may result in another type of noise known as zero crossing
pop noise. This noise may be audible in silent situation when there is no FM modulation in the
receiving signal. This noise is removed by adding resistor R7 at AFCC.
Suitable value for R7 is between 560k and 1M .
AFC RESPONSE TIME
The series RC network connected from AFC pin to VSS, along with decoupling capacitors connected
from AFCC pin 47 to VDD and VSS, determines the attack time of the AFC integration (double) loop.
With the component values shown in page 23, the AFC response time is approximately 16ms.
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