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參數(shù)資料
| 型號(hào)： | MC12149 |
| 廠商： | Motorola, Inc. |
| 英文描述： | Low Power Voltage Controlled Oscillator Buffer(低功耗壓控振蕩器) |
| 中文描述： | 低功耗壓控振蕩器緩沖器（低功耗壓控振蕩器） |
| 文件頁(yè)數(shù)： | 3/12頁(yè) |
| 文件大?。?/td> | 198K |
| 代理商： | MC12149 |
MC12149
3
MOTOROLA RF/IF DEVICE DATA
OPERATIONAL CHARACTERISTICS
A simplified schematic of the MC12149 is found in
Figure 1. The oscillator incorporates positive feedback by
coupling the base of transistor Q2 to the collector of transistor
Q1. In order to minimize interaction between the VCO
outputs and the oscillator tank transistor pair, a buffer is
incorporated into the circuit. This differential buffer is realized
by the Q3 and Q4 transistor pair. The differential buffer drives
the gate which contains the primary open collector outputs, Q
and QB. The output is actually a current which has been set
by an internal bias driver to a nominal current of 4mA.
Additional circuitry is incorporated into the tail of the current
source which allows the current source to be increased to
approximately 10 mA. This is accommodated by the addition
of a resistor which is brought out to the CNTL pin. When this
pin is tied to ground, the additional current is sourced through
the current source thus increasing the output amplitude of the
Q/QB output pair. If less than 10mA of current is needed, a
resistor can be added to ground which reduces the amount of
current.
The Q/QB outputs drive an additional differential buffer
which generate the Q2 output signal. To minimize current, the
circuit is realized as an emitter–follower buffer with an on chip
pull down resistor. This output is intended to drive the
prescaler input of the PLL synthesizer block.
APPLICATION INFORMATION
Figure 2 illustrates the external components necessary for
the proper operation of the VCO buffer. The tank circuit
configuration in this figure allows the VCO to be tuned across
the full operating voltage of the power supply. This is very
important in 3.0 V applications where it is desirable to utilize
as much of the operating supply range as possible so as to
minimize the VCO sensitivity (MHz/V). In most situations, it is
desirable to keep the sensitivity low so the circuit will be less
susceptible to external noise influences. An additional benefit
to this configuration is that additional regulation/ filtering can
be incorporated into the VCC line without compromising the
tuning range of the VCO. With the ac–coupled tank
configuration, the Vtune voltage can be greater than the VCC
voltage supplied to the device.
There are four main areas that the user directly influences
the performance of the VCO. These include Tank Design,
Output Termination Selection, Power Supply Decoupling,
and Circuit Board Layout/Grounding.
The design of the tank circuit is critical to the proper
operation of the VCO. This tank circuit directly impacts the
main VCO operating characteristics:
1)
2)
3)
4)
Frequency of Operation
Tuning Sensitivity
Voltage Supply Pushing
Phase Noise Performance
The tank circuit, in its simplest form, is realized as an LC
circuit which determines the VCO operating frequency. This
is described in Equation 1.
1
2
LC
In the practical case, the capacitor is replaced with a
varactor diode whose capacitance changes with the voltage
applied, thus changing the resonant frequency at which the
VCO tank operates. The capacitive component in Equation 1
also needs to include the input capacitance of the device and
other circuit and parasitic elements. Typically, the inductor is
realized as a surface mount chip or a wound–coil. In addition,
the lead inductance and board inductance and capacitance
also have an impact on the final operating point.
Equation 1
fo
Figure 1. Simplified Schematic
Q3
Q4
Q1
Q2
Q5
Q6
VCC
Q
QB
VCC
GND
VREF
CNTL
136
200
1000
Q2
TANK
VREF
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參數(shù)描述 |
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| MC12149D | 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:LOW POWER VOLTAGE CONTROLLED OSCILLATOR BUFFER |
| MC12149SD | 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:LOW POWER VOLTAGE CONTROLLED OSCILLATOR BUFFER |
| MC1214F | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| MC1214L | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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