PIN二极管通常用于设计控制射频信号路径的开关。串联型PIN电路中的衰减(隔离)随着PIN电阻通过增加正向电流而减小而减小。相反的情况发生在分流配置上。如果控制偏置在高和低(零)值之间快速切换,那么电路就像一个开关。
PIN diodes are often used to design a switch that controls the path of the RF signals. The attenuation (isolation) in the series type PIN circuit is decreased as the resistance of the PIN is reduced by increasing the forward current. The opposite occurs for the shunt configuration. If the control bias is switched rapidly between high and low (zero) values, then the circuit acts simply as a switch.
•SPST(单极单掷)PIN二极管开关的隔离在10MHz时约为50dB,在1GHz时约为15dB。
•由于二极管上的偏压变化,负载电阻作为看到的源也变化;因此,隔离(衰减)主要是通过反射实现的,部分是通过PIN二极管的耗散实现的。
•在并联PIN二极管开关的上频率限制是由二极管寄生电容开始短路负载时插入损耗的增加决定的。然而,可以使用对称匹配电路,通过将二极管电容C合并到低通滤波器中来扩展这个频率限制。
• Isolation of a SPST (single-pole-single-throw) PIN diode switch is about 50dB at 10MHz and about 15dB at 1GHz.
• As the bias on the diode is varied, the load resistance as seen by the source also varies; consequently, the isolation (attenuation) is achieved primarily by reflection and partly by dissipation in the PIN diode.
• The upper frequency limitation in a shunt PIN diode switch is determined by the increase in insertion loss as the diode parasitic capacitance starts to short out the load. However, can be used a symmetrical matching circuit that extends this frequency limitation by incorporating the diode capacitance C, into a low pass filter.
选用电感值L,构成切比雪夫等纹波滤波器。
通过反向偏置降低二极管电容C,
可以获得更高的高频或更低的纹波。
The inductance value L, is chosen to form a Chebyshev equal ripple filter. The upper frequency is determined by the diode capacitance C, by ripple value, and by R.
• Higher upper frequencies or lower ripple may be obtained by lowering the diode capacitance C using reverse bias.
Depending on the performance requirements, the switch can consist of all series diodes, all shunt diodes, or a combination of series and shunt diodes.
根据性能要求,开关可以由所有串联二极管、所有分流二极管或串联和分流二极管的组合组成。
- • Series PIN diode switches are capable of functioning within a wide bandwidth, which is limited by the biasing inductors and DC blocking capacitors. In reverse biased mode the parasitic capacitance of PIN diodes gives rise to poor isolation at microwave frequencies, with a 6dB per octave roll-off versus frequency. In some applications these parasitic elements can be either“tuned-out” by additional external reactance (parallel inductor) which actually is utilized by forming a resonant circuit around the diode. The bandwidth of such structures is, however, limited.
- •系列PIN二极管开关能够在宽带宽内工作,这是受偏置电感和直流阻塞电容的限制。在反向偏置模式下,PIN二极管的寄生电容导致了在微波频率下较差的隔离,每倍频滚转的频率为6dB。在一些应用中,这些寄生元件可以通过额外的外部电抗(并联电感)“调谐”,实际上是通过在二极管周围形成一个谐振电路来利用的。然而,这种结构的带宽是有限的。
- • Shunt PIN diode switches feature high isolation relatively independent of frequency. To turn a switch on, PIN diodes are reversed, and this means a dominant reverse biased capacitance exists. Commonly, designers use a circuit transmission line to create series lumped inductance to achieve a low pass filter effect which enables the switch to work up to the desired frequency. Shunt diodes RF switches have limited frequency bandwidth, arising from the use of theλ/4 transmission lines between the common junction and each shunt diode. At frequency fo, where the transmission lines areλ/4 in length, when diode D1 is forward biased and diode D2 is reverse biased, the RF signal flows from port 3 to port 2, and the RF port 1 will be isolated. Theλ/4 line will transform the short circuit at D1 into an open circuit at the common junction, eliminating any reactive loading at that point. As the frequency is changed from fo, the transmission lines will change in electrical length, creating a mismatch at the common junction.
- •分流PIN二极管开关具有高隔离相对独立于频率。打开一个开关,PIN二极管是反向的,这意味着一个主要的反向偏置电容存在。通常,设计人员使用电路传输线来创建串联集总电感,以实现低通滤波器效果,使开关工作到所需的频率。分流二极管射频开关有有限的频率带宽,由使用λ/4传输线之间的公共结和每个分流二极管。在频率为λ/4的情况下,当二极管D1正向偏置,二极管D2反向偏置时,RF信号从端口3流到端口2,RF端口1被隔离。λ/4线将在D1处的短路转变为在公共结处的开路,消除在那一点上的任何无功负载。当频率从fo改变时,传输线的电气长度将发生变化,在公共结处产生不匹配。
- There are PIN switch designs that use combination of series and shunt diodes (compound switches), and switches that use resonant structures (tuned switches) to improve isolation and insertion loss performance. These switches are more complicated to design and consume higher biasing current compared to series or shunt PIN diode switches.
- 有一些PIN开关设计使用串联和分流二极管的组合(复合开关),以及使用谐振结构的开关(调谐开关),以提高隔离和插入损耗性能。与串联或并联PIN二极管开关相比,这些开关设计更复杂,消耗的偏置电流更高。
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In a PIN diode RF switch design, the biasing path is connected to the RF path of the switch and DC blocking capacitors are needed at the RF ports.
在PIN二极管RF开关设计中,偏置路径连接到开关的RF路径,RF端口需要直流隔离电容。
- The DC blocking capacitors will degrade the insertion loss performance of the PIN diode switch:
- 直流阻塞电容器会降低PIN二极管开关的插入损耗性能:
- at low frequencies due to the high pass filter effect of the capacitor.
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在低频时,由于电容器的高通滤波效应。
- at high frequencies due to SRF (self-resonant frequency), and due to transmission loss through the capacitor.
- 在高频率下,由于SRF(自谐振频率),以及由于通过电容器的传输损耗。
RF chokes (inductors) are used along the biasing paths to avoid RF signal leakage.
射频扼流圈(电感)沿偏置路径使用,以避免射频信号泄漏。
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