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參數資料
| 型號： | MRF1508 |
| 元件分類： | 功率晶體管 |
| 英文描述： | UHF BAND, Si, N-CHANNEL, RF POWER, MOSFET |
| 封裝： | POWER, PLASTIC, CASE 466-02, 4 PIN |
| 文件頁數： | 5/16頁 |
| 文件大小： | 202K |
| 代理商： | MRF1508 |
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MRF1508
MOTOROLA RF DEVICE DATA
APPLICATIONS INFORMATION
DESIGN CONSIDERATIONS
The MRF1508 is a common–source, RF power, N–Channel
enhancement mode, Lateral Metal–Oxide Semiconductor
Field–Effect Transistor (MOSFET). Motorola Application Note
AN211A, “FETs in Theory and Practice”, is suggested reading
for those not familiar with the construction and characteristics
of FETs.
This surface mount packaged device was designed primari-
ly for VHF and UHF portable power amplifier applications.
Manufacturability is improved by utilizing the tape and reel
capability for fully automated pick and placement of parts.
However, care should be taken in the design process to insure
proper heat sinking of the device.
The major advantages of Lateral RF power MOSFETs
include high gain, simple bias systems, relative immunity from
thermal runaway, and the ability to withstand severely
mismatched loads without suffering damage.
MOSFET CAPACITANCES
The physical structure of a MOSFET results in capacitors
between all three terminals. The metal oxide gate structure
determines the capacitors from gate–to–drain (Cgd), and
gate–to–source (Cgs). The PN junction formed during fabrica-
tion of the RF MOSFET results in a junction capacitance from
drain–to–source (Cds). These capacitances are characterized
as input (Ciss), output (Coss) and reverse transfer (Crss)
capacitances on data sheets. The relationships between the
inter–terminal capacitances and those given on data sheets
are shown below. The Ciss can be specified in two ways:
1. Drain shorted to source and positive voltage at the gate.
2. Positive voltage of the drain in respect to source and
zero volts at the gate.
In the latter case, the numbers are lower. However, neither
method represents the actual operating conditions in RF
applications.
Drain
Cds
Source
Gate
Cgd
Cgs
Ciss = Cgd + Cgs
Coss = Cgd + Cds
Crss = Cgd
DRAIN CHARACTERISTICS
One critical figure of merit for a FET is its static resistance
in the full–on condition. This on–resistance, RDS(on), occurs in
the linear region of the output characteristic and is specified
at a specific gate–source voltage and drain current. The
drain–source voltage under these conditions is termed
VDS(on). For MOSFETs, VDS(on) has a positive temperature
coefficient at high temperatures because it contributes to the
power dissipation within the device.
BVDSS values for this device are higher than normally
required for typical applications. Measurement of BVDSS is not
recommended and may result in possible damage to the
device.
GATE CHARACTERISTICS
The gate of the RF MOSFET is a polysilicon material, and
is electrically isolated from the source by a layer of oxide. The
DC input resistance is very high – on the order of 109
—
resulting in a leakage current of a few nanoamperes.
Gate control is achieved by applying a positive voltage to
the gate greater than the gate–to–source threshold voltage,
VGS(th).
Gate Voltage Rating — Never exceed the gate voltage
rating. Exceeding the rated VGS can result in permanent
damage to the oxide layer in the gate region.
Gate Termination — The gates of these devices are
essentially capacitors. Circuits that leave the gate open–cir-
cuited or floating should be avoided. These conditions can
result in turn–on of the devices due to voltage build–up on the
input capacitor due to leakage currents or pickup.
Gate Protection — These devices do not have an internal
monolithic zener diode from gate–to–source. If gate protec-
tion is required, an external zener diode is recommended.
Using a resistor to keep the gate–to–source impedance low
also helps dampen transients and serves another important
function. Voltage transients on the drain can be coupled to the
gate through the parasitic gate–drain capacitance. If the
gate–to–source impedance and the rate of voltage change on
the drain are both high, then the signal coupled to the gate may
be large enough to exceed the gate–threshold voltage and
turn the device on.
DC BIAS
Since the MRF1508 is an enhancement mode FET, drain
current flows only when the gate is at a higher potential than
the source. RF power FETs operate optimally with a quiescent
drain current (IDQ), whose value is application dependent. The
MRF1508 was characterized at IDQ = 150 mA, which is the
suggested value of bias current for typical applications. For
special applications such as linear amplification, IDQ may have
to be selected to optimize the critical parameters.
The gate is a dc open circuit and draws no current.
Therefore, the gate bias circuit may generally be just a simple
resistive divider network. Some special applications may
require a more elaborate bias system.
GAIN CONTROL
Power output of the MRF1508 may be controlled to some
degree with a low power dc control signal applied to the gate,
thus facilitating applications such as manual gain control,
ALC/AGC and modulation systems. This characteristic is very
dependent on frequency and load line.
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相關代理商/技術參數 |
參數描述 |
|---|---|
| MRF15090 | 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:RF POWER TRANSISTOR |
| MRF150J | 功能描述:射頻MOSFET電源晶體管 RoHS:否 制造商:Freescale Semiconductor 配置:Single 晶體管極性: 頻率:1800 MHz to 2000 MHz 增益:27 dB 輸出功率:100 W 汲極/源極擊穿電壓: 漏極連續電流: 閘/源擊穿電壓: 最大工作溫度: 封裝 / 箱體:NI-780-4 封裝:Tray |
| MRF150MP | 制造商:M/A-COM Technology Solutions 功能描述:RF POWER TRANSISTOR MOSFET |
| MRF151 | 功能描述:射頻MOSFET電源晶體管 5-175MHz 150Watts 50Volt Gain 18dB RoHS:否 制造商:Freescale Semiconductor 配置:Single 晶體管極性: 頻率:1800 MHz to 2000 MHz 增益:27 dB 輸出功率:100 W 汲極/源極擊穿電壓: 漏極連續電流: 閘/源擊穿電壓: 最大工作溫度: 封裝 / 箱體:NI-780-4 封裝:Tray |
| MRF1511N | 制造商:FREESCALE 制造商全稱:Freescale Semiconductor, Inc 功能描述:RF Power Field Effect Transistor |
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