欢迎访问ic37.com |
会员登录 免费注册
发布采购

MICRF022YM-FS48 参数 Datasheet PDF下载

MICRF022YM-FS48图片预览
型号: MICRF022YM-FS48
PDF下载: 下载PDF文件 查看货源
内容描述: 300-440MHz QwikRadio系列? ASK接收器 [300-440MHz QwikRadio? ASK Receiver]
分类和应用: 商用集成电路光电二极管
文件页数/大小: 17 页 / 373 K
品牌: MICREL [ MICREL SEMICONDUCTOR ]
 浏览型号MICRF022YM-FS48的Datasheet PDF文件第5页浏览型号MICRF022YM-FS48的Datasheet PDF文件第6页浏览型号MICRF022YM-FS48的Datasheet PDF文件第7页浏览型号MICRF022YM-FS48的Datasheet PDF文件第8页浏览型号MICRF022YM-FS48的Datasheet PDF文件第10页浏览型号MICRF022YM-FS48的Datasheet PDF文件第11页浏览型号MICRF022YM-FS48的Datasheet PDF文件第12页浏览型号MICRF022YM-FS48的Datasheet PDF文件第13页  
Micrel, Inc.  
MICRF002/RF022  
To further enhance duty-cycled operation, the AGC push  
and pull currents are boosted for approximately 10ms  
immediately after the device is taken out of shutdown. This  
compensates for AGC capacitor voltage droop and reduces  
the time to restore the correct AGC voltage. The current is  
boosted by a factor of 45.  
Step 3: Selecting the CTH Capacitor  
Extraction of the dc value of the demodulated signal  
for purposes of logic-level data slicing is accomplished  
using the external threshold capacitor CTH and the on-  
chip switched capacitor “resistor” RSC, shown in the  
block diagram.  
Slicing level time constant values vary somewhat with  
decoder type, data pattern, and data rate, but typically  
values range from 5ms to 50ms. Optimization of the  
value of CTH is required to maximize range.  
Selecting CAGC Capacitor in Continuous Mode  
A CAGC capacitor in the range of 0.47µF to 4.7µF is typically  
recommended. The value of the CAGC should be selected to  
minimize the ripple on the AGC control voltage by using a  
sufficiently large capacitor. However if the capacitor is too  
large the AGC may react too slowly to incoming signals.  
AGC settling time from a completely discharged (zero-volt)  
state is given approximately by Equation 6:  
Selecting Capacitor CTH  
The first step in the process is selection of a data-slicing-  
level time constant. This selection is strongly dependent on  
system issues including system decode response time and  
data code structure (that is, existence of data preamble,  
etc.). This issue is covered in more detail in Application  
Note 22.  
(6)  
t = 1.333CAGC 0.44  
where:  
CAGC sin in µF, and t is in seconds.  
The effective resistance of RSC is listed in the electrical  
characteristics table as 145kat 315MHz, this value scales  
linearly with frequency. Source impedance of the CTH pin at  
other frequencies is given by Equation 4, where fT is in  
MHz:  
Selecting CAGC Capacitor in Duty-Cycle Mode  
Voltage droop across the CAGC capacitor during shutdown  
should be replenished as quickly as possible after the IC is  
enabled. As mentioned above, the MICRF002 boosts the  
push-pull current by a factor of 45 immediately after start-  
up. This fixed time period is based on the reference  
oscillator frequency fT. The time is 10.9ms for fT = 6.00MHz,  
and varies inversely with fT. The value of CAGC capacitor  
and the duration of the shutdown time period should be  
selected such that the droop can be replenished within this  
10ms period.  
4.8970  
(4)  
RSC = 145kΩ  
fT  
τ of 5x the bit-rate is recommended. Assuming that a slicing  
level time constant τ has been established, capacitor CTH  
may be computed using Equation 5:  
τ
(5)  
CTH =  
Polarity of the droop is unknown, meaning the AGC voltage  
could droop up or down. Worst-case from a recovery  
standpoint is downward droop, since the AGC pull-up  
current is 1/10th magnitude of the pulldown current. The  
downward droop is replenished according to the Equation  
7:  
RSC  
A standard ±20% X7R ceramic capacitor is generally  
sufficient. Refer to Application Hint 42 for CTH and CAGC  
selection examples.  
Step 4: Selecting the CAGC Capacitor  
I
V  
t  
The signal path has AGC (automatic gain control) to  
increase input dynamic range. The attack time constant of  
the AGC is set externally by the value of the CAGC capacitor  
connected to the CAGC pin of the device. To maximize  
system range, it is important to keep the AGC control  
voltage ripple low, preferably under 10mVPP once the  
control voltage has attained its quiescent value. For this  
reason capacitor values of at least 0.47µF are  
recommended.  
(7)  
=
CAGC  
where:  
I = AGC pullup current for the initial 10ms (67.5µA)  
AGC = AGC capacitor value  
C
t = droop recovery time  
V = droop voltage  
For example, if user desires t = 10ms and chooses a  
4.7µF CAGC, then the allowable droop is about 144mV.  
Using the same equation with 200nA worst case pin  
leakage and assuming 1µA of capacitor leakage in the  
same direction, the maximum allowable t (shutdown time)  
is about 0.56s for droop recovery in 10ms.  
The AGC control voltage is carefully managed on-chip to  
allow duty-cycle operation of the MICRF002. When the  
device is placed into shutdown mode (SHUT pin pulled  
high), the AGC capacitor floats to retain the voltage. When  
operation is resumed, only the voltage droop due to  
capacitor leakage must be replenished. A relatively low-  
leakage capacitor is recommended when the devices are  
used in dutycycled operation.  
The ratio of decay-to-attack time-constant is fixed at 10:1  
(that is, the attack time constant is 1/10th of the decay time  
constant). Generally the design value of 10:1 is adequate  
M9999-070808  
July 2008  
9