- 您现在的位置：买卖IC网 > Sheet目录477 > MICRF501BLQ TR (Micrel Inc)TXRX SGL 300-600MHZ 44-LQFP
MICRF501
signals. The receive mode loop filter comprises C115, C116,
R109, R101 and C101.
Modulation Outside PLL (Open Loop)
In this mode the charge pump output is tri-stated. The loop is
open and will therefore not track the modulation. This means
that the loop filter can have a relatively high bandwidth, which
give short switching times. However, the loop voltage will
decrease with time due to current leakage. The transmit time
will therefore be limited and is dependent on the bandwidth of
the loop filter. High bandwidth gives low capacitor values and
the loop voltage will decrease faster, which gives a shorter
transmit time.
The loop is closed until the PLL is locked on the desired
frequency and the power amplifier is turned on. The loop
immediately opens when the modulation starts. The loop will
not track the modulation, but the modulation still needs to be
DC free due to the AC coupling in the modulation network.
Transmit
Power Amplifier (PA)
The power amplifier is biased in class AB. The last stage has
an open collector, and an external load inductor (L5) is
therefore necessary. The DC current in the amplifier is
adjusted with an external bias resistor (R14). A good starting
point when designing the PA is a 1.5k ? bias resistor which
gives a bias current of approximately 50 μ A. This will give a
bias current in the last stage of about 15mA. R14 is optimized
to 1k ? , as shown in the application circuit.
The impedance matching circuit will depend on the type of
antenna used, but should be designed for maximum output
power. For maximum output power the load seen by the PA
must be resistive and should be about 100 ? . The output
power is programmable in eight steps, with approximately
3dB between each step. This is controlled by bits Pa2 - Pa0.
To prevent spurious components from being transmitted the
PA should be switched on/off slowly, by allowing the bias
current to ramp up/down at a rate determined by the external
capacitor C25 connected to Pin 24. The ramp up/down
current is typically 1.1 μ A, which makes the on/off rate for a
2.8V power supply 2.6 μ s/pF. Turning the PA on/off affects the
PLL. Therefore the on/off rate must be adjusted to the PLL
bandwidth.
PA Buffer
A buffer amplifier is connected between the VCO and the PA
Micrel
stabilizes the overall dc feedback loop, which has a large low
frequency loop gain. Figure 8 shows the input impedance of
the LNA.
Figure 8. Input Impedance
Input matching is very important to get high receive sensitiv-
ity. The LNA can be bypassed by setting bit LNA to ‘ 1 ’ . This
is useful for very strong signal levels. The RSSI signal can be
used to drive a microcontroller to create a subroutine when a
strong income signal is present to bypass the LNA. This will
increase the dynamic range by approximately 25dB.
The mixers have a gain of about 15dB at 434MHz. The
differential outputs of the mixers are available at Pins 34, 35
and at Pins 38, 39. The output impedance of each mixer is
about 30k ? .
Sallen-Key Filter and Preamplifier
Each channel includes a preamplifier and a prefilter, which is
a three-pole elliptic Sallen-Key lowpass filter with 20dB
stopband attenuation. It protects the following gyrator filter
from strong adjacent channel signals. The preamplifier has a
gain of 35dB and output voltage swing is about 200mV PP .
The third order Sallen-Key lowpass filter is programmable to
four different cut-off frequencies according to the table below:
Fc1 Fc0 Cut-Off Frequency Recommended
(kHz) Channel Spacing
0 0 10 ± 2.5 25kHz
0 1 30 ± 7.5 100kHz
to ensure that the input signal of the PA has sufficient
1
0
60 ± 15
200kHz
amplitude to achieve the desired output power. This buffer
can be bypassed by setting the bit Gc to 0.
Receive
Front End (LNA and Mixers)
A low noise amplifier in the RF receiver is used to boost the
incoming signal prior to the frequency conversion process.
This is important in order to prevent mixer noise from domi-
nating the overall front end noise performance. The LNA is a
two stage amplifier and has a nominal gain of 25dB at
434MHz. The LNA has a dc feedback loop, which provides
bias for the LNA. The external capacitor C26 decouples and
1 1 200 ± 50 700kHz
For the 10kHz cut-off frequency the first pole must be gener-
ated externally by connecting a 330pF capacitor between the
outputs of each mixer.
As the cut-off frequency of the gyrator filter can be set by
varying an external resistor, the optimum channel spacing
will depend on the cut-off frequencies of the Sallen-Key filter.
The table above shows the recommended channel spacing
depending on the different bit settings.
MICRF501
12
March 2003
发布紧急采购，3分钟左右您将得到回复。
相关PDF资料
MICRF505DEV1
KIT DEV RADIOWIRE 850-950MHZ
MICRF506DEV1
EVAL BOARD EXPERIMENTAL MICRF506
MICRF507YML TR
TXRX FSK LOW PWR W/AMP 32MLF
MICRF600DEV1
KIT DEV RADIOWIRE 902-928MHZ
MK01-C
SENSOR REED SPST-NO SMD
MK01-H
SENSOR REED SPDT-CHANGE SMD
MK02/0-1A66-500W
SENSOR REED SPST-NO
MK02/6-0
SENSOR REED PCB 24MM T/H
相关代理商/技术参数
MICRF501EVAL1
功能描述:EVAL BOARD EXPERIMENTAL MICRF501 RoHS:否 类别:RF/IF 和 RFID >> RF 评估和开发套件，板 系列:RadioWire® 标准包装:1 系列:- 类型:GPS 接收器 频率:1575MHz 适用于相关产品:- 已供物品:模块 其它名称:SER3796
MICRF505
制造商:MICREL 制造商全称:Micrel Semiconductor 功能描述:868MHz and 915MHz ISM Band Transceiver
MICRF505_07
制造商:MICREL 制造商全称:Micrel Semiconductor 功能描述:850MHz and 950MHz ISM Band Transceiver
MICRF505BML
制造商:Rochester Electronics LLC 功能描述: 制造商:RF Micro Devices Inc 功能描述:
MICRF505BML TR
功能描述:TXRX ISM 868-915MHZ 32-MLF RoHS:否 类别:RF/IF 和 RFID >> RF 收发器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program 标准包装:30 系列:- 频率:4.9GHz ~ 5.9GHz 数据传输率 - 最大:54Mbps 调制或协议:* 应用:* 功率 - 输出:-3dBm 灵敏度:- 电源电压:2.7 V ~ 3.6 V 电流 - 接收:* 电流 - 传输:* 数据接口:PCB，表面贴装 存储容量:- 天线连接器:PCB，表面贴装 工作温度:-25°C ~ 85°C 封装/外壳:68-TQFN 裸露焊盘 包装:管件
MICRF505DEV1
功能描述:射频开发工具 MICRF505 Evaluation Kit - For experimental use only
RoHS:否 制造商:Taiyo Yuden 产品:Wireless Modules 类型:Wireless Audio 工具用于评估:WYSAAVDX7 频率: 工作电源电压:3.4 V to 5.5 V
MICRF505DEV1
制造商:Micrel Inc 功能描述:KIT MICRF505 EVALUATION
MICRF505L
制造商:MICREL 制造商全称:Micrel Semiconductor 功能描述:850MHz and 950MHz ISM Band Transceiver