English:
[0001] This present invention relates to microwave switches, and in particular, to absorptive microwave switches.
[0002] Absorptive switches are attractive components for a system designer, as the input, and ideally output, reflection coefficient of the switch remains constant regardless of the state of the switch. This reduces the effects of the switch on system parameters such as frequency pulling of a signal source, or the inducement of other transient effects that can be problematic in very short interval time-based systems.
[0003] One drawback of absorptive switches is that a dummy, or additional load, has to be included in the circuitry to be presented to the input network to absorb any incident energy when the switch is selected to be in a non-transmit or isolated state. This dummy load takes up valuable circuit board space in an integrated circuit (IC) design that directly translates to increased circuit cost and reduced yield.
[0004] Thus, there is presently a need for an absorptive switch which does not utilize a dummy load.
[0005] An embodiment of the present invention comprises a switch circuit including a first differential amplifier pair providing a portion of an isolation channel, a second differential amplifier pair providing a portion of a transmit channel, and a third differential amplifier pair providing a control bias for selecting either the transmit channel or the isolation channel.
[0006] An embodiment of the present invention also comprises a method for providing isolation between the input and output of a circuit comprising the steps of providing a first channel including at least one first differential amplifier pair, said first channel providing isolation between the input and output of the circuit, providing a second channel including at least one second differential amplifier pair, said second channel providing coupling between the input and output of the circuit, and providing a control bias which selects one of the first channel or the second channel.
[0008] Figure 2 shows the switch circuit of Figure 1 implemented as an integrated circuit.
[0009] Figure 3(a) is a graph showing a frequency versus decibel (dB) response of the input reflection coefficient for the switch circuit of Figure 1 in both the isolated and transmission states.
[0010] Figure 3(b) is a graph showing shows a frequency versus decibel (dB) response of the transmission characteristics for the switch circuit of Figure 1 when the switch circuit is in alternately the isolated and the "transmit" states.
[0011] An embodiment of the present invention comprises an absorptive microwave switch circuit that provides 35 decibels (dB) of isolation between input and output over 15 Gigahertz (GHz)-26GHz range, yet is only 500 micrometers (μm) by 250μm in size. Since 24GHz has been used recently to provide pulsed radar systems for short-range automotive sensors, the present invention will be particularly applicable to such systems. The switch circuit ensures that there is almost no perceptible change in the input reflection coefficient between the transmission or absorptive states. In the transmit state the switch provides gain for the input signal between 14.2GHz and 25.5GHz, and has a ldB loss bandwidth of over 12GHz. Lastly, the use of a constant current biasing scheme allows extremely fast switching between states allowing the switch to be used to generate pulses of 200 picoseconds (pS) in length with rise and fall times of approximately 60pS. The entire switch, including biasing circuitry, requires only 12 milliamp (mA) from a +5 volt (V) supply.
[0012] As discussed above, the present invention will be particularly applicable to automotive sensing systems, which are required to detect objects at distances between 5 centimeters (cm) and 10 meters (m) to 30m, often with a distance resolution of less than 10cm. These requirements translate directly to a minimum inter-pulse period of less than 2 nanoseconds (nS) (correspond to the two-way flight time of a pulse reflected from an object 10cm from the sensor), and a required pulse width of less than 500pS. These design considerations require a circuit which has fast switching.
[0013] Figure 1 shows an absorptive single pole single throw (SPST) switch circuit 100 according to an exemplary embodiment of the present invention which includes an input terminal Vjn, and output terminal Vout. and a control terminal Vcontroi- The switch circuit 100 also includes a first differential amplifier pair 110 including transistors Ql and Q2, a second differential amplifier pair 120 including transistors Q3 and Q4, and a third differential amplifier pair 130 including transistors Q5 and Q6. The collectors of each of transistors Ql- Q4 are all coupled to a supply voltage Vcc. Transistors Q3 and Q4 further include inductors 140, 150 coupled between the collectors and Vcc- The collector of transistor Q5 is coupled to the emitters of transistors Ql and Q2, and the collector of transistor Q6 is coupled to the emitters of transistors Q3 and Q4. The emitters of transistors Q5 and Q6 are coupled to a current source Iee.
[0014] In operation, transistor Q6 is biased on by control signal Vcontroi to select the "transmit" state of the switch 100. This is accomplished by providing a control signal Vcontroi which is above the junction voltage of transistor Q6 on the negative side (e.g., -0.7 volts). In the "transmit" state, signals entering input terminal Vmare coupled to output terminal Vout- The biasing on of transistor Q6 in turn biases on transistors Q3 and Q4, thus creating a signal path from the input terminal Vjnto the output terminal Voutat the respective collectors of transistors Q3 and Q4. Thus, the input signal is transmitted to the output.
[0015] Alternatively, if Vcontroi selects the "isolation" state of the switch 100 by biasing transistor Q5 on, signals entering input terminal Vjnare decoupled from output terminal Vout. As with the "transmit" state, this is accomplished by providing a control signalcontroi which is above the junction voltage of transistor Q5 on the positive side (e.g., +0.7 volts). The biasing on of transistor Q5 in turn biases on transistors Ql and Q2, and thus creates a signal path from the input terminal Vjnto the midpoint between the bases of transistors Q2 and Q3. Accordingly, the input is "isolated" from the output.
[0016] In the "transmit" state, the high input impedance of the transistor pair Ql, Q2 when turned off minimizes the circuit loading on Q3 and Q4, and the circuit appears as a standard differential amplifier, that when matched, can provide gain to an input signal. Bias chokes in the form of inductors 140, 150 used to isolate the DC voltage supply Vccfrom the output microwave signal Vout-
[0017] In the "isolation" state, the high impedance presented by Q3 and Q4 is such that they load input circuit only lightly. The input voltage Vjnis transferred primarily to the Ql, Q2 pair where it sees a virtual RF ground. The differential pair Ql, Q2 can thus be considered as an ideal unilateral amplifier.
[0018] The switch circuit 100 provides for several advantages. First, the control signal Vcontroi applied differentially across transistors Q5 and Q6 allows for easy selection of either the transmission or isolated state. Additionally, the constant current steering between the two differential amplifier pairs 110, 120 ensures extremely high speed switching between the two states, as the switch never has to be depleted of high current densities. In particular, the switch circuit provides a pulse width of approximately 220pS, with rise and fall times around 60pS at 24 GHz.
[0019] The switch circuit 100 may be implemented using any commercially available transistor based semiconductor process, such as a Silicon Germanium (SiGe) process (e.g., Atmel SiGE2basic).
[0020] Figure 2 shows a photograph of the switch circuit 100 of Figure 1 implemented in SiGe. As should be understood by those of ordinary skill in the art, the switch circuit 100 may be implemented in other substrates as well, such as Silicon Gallium Arsenide (SiGaAs) or Indium Phosphide (InP). As shown in Figure 2 the switch circuit also includes input and output matching networks (not shown in the idealized circuit diagram of Figure 1) comprising a series of inductors and resistors designed for operation at a center frequency of 24GHz. The first and second differential amplifier pairs 110, 120 are disposed adjacent to each other and connected in parallel across an input signal network. The collectors of Q3-Q4 are connected to an output-matching network, while the collectors of Ql- Q2 are connected directly together and further connected directly to source voltage Vcc. The total circuit area of the switch circuit shown in Figure 2 including input and output matching networks and bias circuits is 500μm by 250 μm.
[0021] Figure 3(a) shows the input reflection coefficient of the switch circuit 100 in both its transmission and absorption (isolation) states. The difference between the reflection coefficients in each state is extremely small, as the DC current flowing through the network has remained constant. This validates using the virtual radiofrequency (RF) ground of the differential pair Q1-Q2 as a load rather than the more conventional technique of steering the input signal into a matched load to provide the absorptive condition. In the transmit state, shown in Figure 3(b), an ON-OFF ratio of over 30dB is achieved over 14GHz-28GHz, and a ldB insertion-loss bandwidth of over 12GHz is measured.
[0022] Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly to include other variants and embodiments of the invention which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.

中文:
[0001]本发明涉及微波开关,具体地说,涉及吸收式微波开关(absorptivemicrowave switch)。
[0002]吸收式开关对于系统设计者是有吸引力的部件,作为输入,且理想的是作为输出,开关的反射系数保持恒定,而与开关的状态无关。这减少了开关对诸如信号源的频率牵引的系统参数的影响,或者其他瞬时效应的引入,其在基于很短间隔时间的系统中可能是有问题的。
[0003]吸收式开关的一个缺陷在于:在将开关选择为处于非传输或隔离状态时,不得不将假(dummy)或附加的负载引入要出现在输入网络的电路中,以吸收任何入射能。该假负载占用了集成电路(IC)设计中的宝贵的电路板空间,这直接转化为增加的电路成本和降低的成品率。
[0004]因此,目前存在对一种不利用假负载的吸收式开关的需求。
[0005]本发明的实施例包括:一种开关电路,其包括第一差分放大器对,用于提供一部分隔离通道,第二差分放大器对,用于提供一部分传输通道,和第三差分放大器对,用于提供用来选择传输通道或隔离通道(isolation channel)的控制偏置。
[0006]本发明的实施例还包括:一种用于在电路的输入和输出之间提供隔离的方法,包括步骤:提供包括至少一个第一差分放大器对的第一通道,所述第一通道提供在电路的输入和输出之间的隔离,提供包括至少一个第二差分放大器对的第二通道,所述第二通道提供在电路的输入和输出之间的耦合,以及提供用于选择第一通道或第二通道之一的控制偏置。
[0008]图2示出了实现为集成电路的图1的开关电路。
[0009]图3(a)是示出了在隔离和传输两个状态下图1的开关电路的输入反射系数的频率相对于分贝(dB)响应的曲线图。
[0010]图3(b)是示出了当开关电路交替处于隔离和“传输”状态下时图1的开关电路的传输特性的频率相对于分贝(dB)响应的曲线图。
[0011]本发明的实施例包括吸收式微波开关电路,其在15千兆赫兹(GHz)至26GHz的范围上在输入和输出之间提供35分贝(dB)的隔离,仍仅为500微米(μm)×250μm的大小。由于最近已经将24GHz用于提供用于近程汽车传感器的脉冲雷达系统,所以本发明尤其将被应用于这样的系统。开关电路保证了:在传输或吸收状态之间在输入反射系数中几乎不存在可察觉的变化。在传输状态下,开关为在14.2GHz和25.5GHz之间的输入信号提供了增益,并且具有超过12GHz的1dB损耗带宽。最后,恒定偏流方案的使用使得状态之间的切换极快,这使得开关被用来产生上升与下降时间为大约60微微秒(pS)的、长度为200pS的脉冲。包括偏置电路的整个开关仅需来自+5伏(V)电源的12毫安(mA)。
[0012]如上所述,本发明尤其将被应用于汽车传感系统,需要其通常以小于10cm的距离分辨能力,检测距离在5厘米(cm)和10米(m)至30m之间的物体。这些要求直接转化为小于2纳秒(ns)的最小脉冲间周期(对应于从距离传感器10cm的物体反射的脉冲的双向飞行时间),以及小于500pS的所需脉冲宽度。这些设计因素需要具有快切换的电路。
[0013]图1示出了根据本发明的示例性实施例的、吸收式单刀单掷(SPST)开关电路100,其包括输入端子Vin和输出端子Vout以及控制端子Vcontrol。开关电路100还包括:包括晶体管Q1和Q2的第一差分放大器对110、包括晶体管Q3和Q4的第二差分放大器对120、和包括晶体管Q5和Q6的第三差分放大器对130。晶体管Q1至Q4的每一个的集电极都耦合到电源电压Vcc。晶体管Q3和Q4还包括耦合在集电极和Vcc之间的电感器140、150。晶体管Q5的集电极被耦合到晶体管Q1和Q2的发射极,而晶体管Q6的集电极被耦合到晶体管Q3和Q4的发射极。晶体管Q5和Q6的发射极被耦合到电流源Icc。
[0014]在操作中,由控制信号Vcontrol给晶体管Q6加偏置以使其导通来选择开关100的“传输”状态。这是通过提供高于负侧上的晶体管Q6的结电压(例如,-0.7伏)的控制信号Vcontrol来实现的。在“传输”状态下,进入输入端子Vin的信号被耦合到输出端子Vout。晶体管Q6的偏压导通依次给晶体管Q3和Q4加偏置以使其导通,从而创建从输入端子Vin到在晶体管Q3和Q4的各个集电极处的输出端子Vout的信号路径。因此,输入信号被传输到输出。
[0015]或者,如果Vcontrol通过给晶体管Q5加偏置以使其导通来选择开关100的“隔离”状态,则进入输入端子Vin的信号与输出端子Vout去耦合。与“传输”状态下的相同,这是通过提供高于正侧上的晶体管Q5的结电压(例如,+0.7伏)的控制信号Vcontrol来实现的。晶体管Q5的偏压导通依次给晶体管Q1和Q2加偏置以使其导通,从而创建从输入端子Vin到晶体管Q2和Q3的基极之间的中点的信号路径。因此,输入与输出“隔离”。
[0016]在“传输”状态下,当截止时晶体管对Q1、Q2的高输入阻抗最小化了Q3和Q4上的电路负载,并且电路表现为标准的差分放大器,其在匹配时,可以给输入信号提供增益。以电感器140、150为形式的偏置扼流(bias choke)用来将DC电压源Vcc与输出微波信号Vout隔离。
[0017]在“隔离”状态下,由晶体管Q3和Q4呈现的高阻抗使得其仅给输入电路轻微加载。输入电压Vin主要被传送给Q1、Q2对,其中该Q1、Q2对当作虚拟的RF地。因而,差分对Q1、Q2可以被看作理想的单向放大器。
[0018]开关电路100提供了几个优点。首先,经过晶体管Q5和Q6有区别地施加控制信号Vcontrol使得能够容易地选择传输状态或隔离状态。此外,由于开关从来不必耗尽高电流密度,所以在两个差分放大器对110、120之间的恒定电流引导(steering)确保了在两个状态之间的极高速度的切换。特别地,开关电路提供了在24GHz时上升与下降时间为大约60pS的、大约220pS的脉冲宽度。
[0019]开关电路100可以使用任何基于商业上可用的晶体管的半导体处理工艺,诸如硅锗(SiGe)处理工艺(例如,Atmel SiGE2basic),来实现。
[0020]图2示出了以SiGe实现的图1的开关电路100的照片。如本领域技术人员应该理解的,也可以以其它衬底,诸如硅镓砷(SiGaAs)或铟磷化物(InP)来实现。如图2中所示,开关电路还包括:输入和输出匹配网络(在图1的理想电路图中未示出),其包括为以24GHz的中心频率运行而设计的一系列电感器和电阻器。将第一和第二差分放大器对110、120放置成彼此相邻,并经过输入信号网络并联。Q3-Q4的集电极连接到输出匹配网络,同时Q1-Q2的集电极直接连接在一起,并进一步直接连接到源电压Vcc。包括输入和输出匹配网络和偏置电路的、图2中所示的开关电路的整个电路区域是500μm×250μm。
[0021]图3(a)示出了在开关电路100的传输和吸收(隔离)两种状态下其输入反射系数。由于流经网络的DC电流已保持恒定,所以在每种状态下反射系数之间的差异是极小的。通过将差分对Q1-Q2的虚拟射频(RF)地用作负载,而不是将输入信号引导到匹配的负载中以提供吸收条件的更常规的技术,来使其生效。在传输状态下,如图3(b)所示,在14GHz-28GHz上实现了超过30dB的导通-截止比,并且测量到超过12GHz的1dB插入损耗带宽。
[0022]尽管已通过示例性实施例描述了本发明,但是本发明不限于此。相反,所附的权利要求应当被更广泛地解释以包括本发明的其它变化和实施例,其可由本领域技术人员在不背离本发明的等同物的保护范围和变化范围的情况下来做出。