收藏本站
MICRF501
Applications Information
VCO and PLL Section
DIFV DD
Micrel
The frequency synthesizer consists of a VCO, crystal oscilla-
tor, dual-modulus prescaler, programmable frequency divid-
C36
1n
Pin 12
ers, phase-detector, charge pump, lock detector and an
external loop filter. The dual-modulus prescaler divides the
VCO-frequency by 32/33. This mode is controlled by the A-
10MHz
C20
2-6p
C22
5.6p
Pin 13
XOSCOUT
divider. There are two sets of M, N and A-frequency dividers.
Using both sets in transmit mode, FSK can be implemented
by switching between those two sets. The phase-detector is
a frequency/phase detector with back slash pulses to mini-
mize phase noise. The VCO, crystal oscillator, charge pump,
lock detector and the loop filter will be described in detail
below.
Voltage Controlled Oscillator (VCO)
C21
47p
DIGGND
Figure 4. Crystal Oscillator
The crystal oscillator is tuned by varying the trimming capaci-
tor C20. The drift of the RF frequency is the same as the drift
of crystal frequency when measured in ppm. The total differ-
ence in ppm, ? f(ppm), between the tuned RF frequency and
C13
VDD
Pin 5
R7
3.6k
the drifted frequency is given by:
? f(ppm) = S T × ? T + n × ? t
where:
loopfilter_output
R8
47k
D1
MA4ST350
L1
47nH
C35
2.2p
15p
Pin 6
OSCOUT
?
?
S T is the total temperature coefficient of the oscillator
frequency (due to crystal and components) in ppm ° C.
? T is the change in temperature from room
temperature, at which the crystal was tuned.
Pin 7
?
n is the ageing in ppm/year.
Figure 3. VCO
?
? t is the time (in years) elapsed since the transceiver
was last tuned.
The circuit schematic of the VCO with external components
is shown in Figure 3. The VCO is basically a Colpitts oscilla-
tor. The oscillator has an external resonator and varactor.
The resonator consists of inductor L1 and the series connec-
tion of capacitor C13, the internal capacitance, the capaci-
tance of the varactor and C35 in parallel with D1. The
capacitance of the varactor (D1) decreases as the input
voltage increases. The VCO frequency will therefore in-
crease as the input voltage increases. The VCO has a
positive gain (MHz/Volt). C35 is added, if necessary, to bring
VCO tuning voltage to its middle range or VCC/2, which is
measured at Pin 9 - CMPOUT.
If the value of capacitor C13 and C14 become too small the
amplitude of the VCO signal decreases, which leads to lower
output power.
The layout of the VCO is very critical. The external compo-
nents should be placed as close to the input pin (Pin 6) as
possible. The anode of the varactor D1 must be placed next
to pins 7 and 8. Ground vias should be next to component
pads.
Crystal Oscillator
The crystal oscillator is the reference for the RF output
frequency as well as for the LO frequency in the receiver. The
crystal oscillator is a very critical block since very good phase
and frequency stability is required. The schematic of the
crystal  oscillator  with  external  components  for  10MHz  is
shown in Figure 4. These components are optimized for a
crystal with 15pF load capacitance.
The demodulator will not be able to decode data when
? f(Hz) = ? f(ppm) × f RF is larger than the FSK frequency
deviation. For small frequency deviations, the crystal should
be pre-aged, and should have a small temperature coeffi-
cient. The circuit has been tested with a 10MHz crystal, but
other crystal frequencies can be used as well.
The circuit has been tested with a 10MHz crystal, but other
crystal frequencies can be used as well.
Prestart of XCO
The start-up time of a crystal oscillator is typically some
milliseconds. Therefore, to save current consumption, the
MICRF501 circuit has been designed so that the XCO is
turned on before any other circuit block. During start-up the
XCO amplitude will eventually reach a sufficient level to
trigger the M-counter. After counting two M-counter output
pulses the rest of the circuit will be turned on. The current
consumption during the prestart period is approximately
300 μ A.
Lock Detector
The MICRF501 circuit has a lock detector feature that indi-
cates whether the PLL is in lock or not. A logic high on Pin 15
(LOCKDET) means that the PLL is in lock.
The phase detector output is converted into a voltage that is
filtered by the external capacitor C23, connected to Pin 14,
LDC. The resulting DC voltage is compared to a reference
window set by bits Ref0 – Ref5. The reference window can be
stepped up/down linearly between 0V, Ref0 – Ref5 =1, and
Ref0 – Ref5 = 0, which gives the highest value (DC voltage)
of the reference window. The size of the window can either be
March 2003
9
MICRF501
发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

*型号 *数量 厂商 批号 封装
添加更多采购

我的联系方式

*
*
*
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