Abstract:
A wafer probe with built in components to perform frequency multiplication, upconversion, downconversion, and mixing typically performed by an RF module of a vector network analyzer (VNA). The wafer probe is designed for testing integrated circuits used in collision avoidance radar systems and operates over the 76-77 GHz frequency range allocated by the Federal Communications Commission (FCC) for collision avoidance radars. To minimize costs, the wafer probe preferably utilizes integrated circuits for frequency multiplication, upconversion, downconversion, and mixing manufactured for collision avoidance radar systems.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to components for a vector network analyzer (VNA) and wafer probe which may be used to test integrated circuits manufactured for an automobile collision avoidance radar. 
     2. Description of the Related Art 
     Recently, automobile manufacturers, have provided collision avoidance radar systems in a limited number of vehicle models. Collision avoidance radar systems have also recently been made available for purchase by consumers for installation on trucks or automobiles. An example of such a system is the Eaton® VORAD® Collision Warning System available from Eaton VORAD Technologies, L.L.C., of San Diego, Calif. 
     Collision avoidance radar systems currently available operate by transmitting and receiving signals using an antenna located in the front grill area of a vehicle. The collision avoidance radar determines from a delay before a return signal is received, or from a frequency shift in a signal received, a distance an object causing the return signal is located from the vehicle and how fast the object is traveling relative to the vehicle. 
     Collision avoidance radar systems typically operate within a narrow frequency band. In the United States, the Federal Communications Commission (FCC) has allocated the frequency range of 76-77 GHz for collision avoidance radars. 
     A VNA is typically used with an attached wafer probe to test microwave integrated circuit components manufactured for a collision avoidance radar. A traditional VNA is an expensive system designed to operate over a wide range of frequencies. FIG. 1 shows a block diagram of typical components included in a VNA. As shown, the VNA includes signal sources  100 - 101 , a test set  102 , test modules  104 - 105 , and a VNA controller  108 . 
     A typical signal source which may be used for the LO signal source  100  and RF signal source  102  for a VNA is the Anritsu model 68037B, manufactured by Anritsu Company of Morgan Hill Calif. The 68037B signal source operates over a 2-20 GHz frequency range and provides power up to +17 dBm. The frequencies for the signal sources  100 - 101  are controlled by VNA controller  108  through signals over a general purpose interface bus (GPIB). An example of a VNA controller is the 37100A manufactured by Anritsu Company. 
     The LO signal from signal source  100  and the RF signal from signal source  101  are provided to a test set  102 , such as the 3735A test set manufactured by Anritsu Company. Components included in the test set are shown in FIG.  2 . The test includes a transfer switch  200  which selectively provides the RF drive signal from the RF signal source  101  to either the RF port  1  which connects to RF module  104 , or to the RF port  2  which connects to the RF module  105 . The transfer switch  200  is controlled by a signal received from the VNA controller  108 . A power divider  202  provides the LO signal from the LO signal source  100  to the LO ports of the RF modules  104  and  105 . The test set  102  further includes a power supply  204  and a printed circuit board (PCB) assembly  206 . The power supply  204  converts a standard 115V AC signal to 12V and 15V DC signals. The PCB assembly  206 , then provides further voltage regulation and distributes 12V and 15V signals to the RF modules  104  and  105  and forwards the transfer switch control signal to the transfer switch  200 . The test set  102  further forwards the test IF and reference IF signals from the RF modules  104  and  105  to the VNA controller  108  as S-Parameter signals a 1 , a 2 , b 1 , and b 2 . 
     Components for RF modules  104  and  105  are shown in FIG.  3 . An example of the RF module shown is the Anritsu 3741A-X millimeter wave module. The RF module of FIG. 3 contains multipliers  300  and  302  to enable a maximum 20 GHz output from the RF signal source  101  to be multiplied up to 80 GHz to provide coverage of the 76-77 GHz bandwidth for collision avoidance radar systems. Amplifier  304  serves to boost the input signal to the multiplier, while the output of multiplier  300  is amplified by amplifier  306 . Amplifiers  304  and  306  receive power from the +12V output of the test set  102 . Although the multipliers  300  and  302  are shown as times two (×2) devices, the multiplication factor is altered in test sets designed to cover frequency bands other than the 76-77 GHz bandwidth for collision avoidance radars. 
     An RF test signal is provided from multiplier  302  through dual directional coupler  308  to a test port as a test signal. The dual directional coupler  308  serves to provide both the test signal and a reference signal for analysis. The reference signal is provided from a first directional coupler in the dual coupler  308  which couples an incident signal provided from the RF signal source  101  through multipliers  300  and  302  and amplifiers  304  and  306  to a harmonic mixer  310 . The test signal is received from a second coupler in dual coupler  308  which couples a transmitted or reflected signal from the test port to a harmonic mixer  312 . The test signal results from reflections from a test device connected to the test port which will occur if an impedance mismatch exists. When a mismatch occurs, some of the test signal incident at the port will travel into the test device, and some will be reflected back to the test port. The transfer switch  200  of the test set  102  may provide the test signal through another RF module to measure parameters of a two port test device. With a test signal provided from a second RF module in a two port device, the portion of the signal that travels through the test device goes to the test port of the first RF module for measurement. 
     The harmonic mixers  310  and  312  mix the RF signals from the dual directional coupler  308  with the LO signal provided to the mixers through amplifier  313  and power divider  314  to downconvert the RF test and reference signals to 270 MHZ intermediate frequency (IF) signals TEST IF and REF IF. The amplifier  313  is a limiting amplifier used to keep the LO power at a fixed level into the harmonic mixers. The amplifier  320  provides the TEST IF signal from mixer  312 , while the amplifier  322  provides the REF IF signal from the mixer  310 . Amplifiers  313 ,  320 , and  322  receive power from the +15V output of the test set  102 . The TEST IF and REF IF signals are provided from the RF modules  104 - 105  to the VNA controller  108  via the test set  102 . The TEST IF signal carries embedded magnitude and phase information relative to the REF IF signal. 
     An example of the VNA controller is the Anritsu 37100A. A typical VNA controller includes synchronous detectors, a digital signal processor or microprocessor, and a display. The synchronous detectors convert the TEST IF and REF IF signals to digital signal data. The VNA processor controlled by embedded firmware coupled with system software, manipulates this digital data. Resultant S-Parameter data characterizing the test device is then presented on the display, and can also be output to a printer or plotter, or routed to the rear panel external GPIB interface. 
     A wafer probe is an accessory which may be attached to test ports of a VNA enabling the VNA to be used to measure components for a wafer. Measurements on a wafer are performed before wafer circuits are separated or diced. 
     SUMMARY OF THE INVENTION 
     The present invention was developed with recognition that with a potential increase in demand for collision avoidance radar systems, it will be desirable to have a test system operating over a narrow bandwidth of the collision avoidance radar system to reduce test equipment cost. 
     The present invention was further developed with recognition that millimeter microwave integrated circuits (MMICs) used in collision avoidance radar systems are similar to components required in the RF module of a VNA, and the MMICs will operate over the narrow collision avoidance radar frequency range of 76-77 GHz. The present invention was further developed with recognition that the MMICs for collision avoidance radar systems multiply the signal source frequency so that a low cost low frequency signal source can be used to create a signal in the 76-77 GHZ range. The most complex and expensive parts of the VNA are in its signal sources and RF module, particularly for a VNA operating over a wide range of millimeter microwave frequencies. With increasing numbers of collision avoidance radar systems, the cost of MMICs used in the radar has been reduced, and is expected to be reduced further with increasing demand over time. 
     The present invention is a wafer probe with built in components to perform frequency multiplication, upconversion, downconversion and mixing typically performed by a RF module of a VNA. The wafer probe is designed for testing integrated circuits used in collision avoidance radar systems and operates over a slightly wider bandwidth than the 76-77 GHz frequency range allocated by the FCC for collision avoidance radars. By operating only near the 76-77 GHz collision avoidance radar frequency, the RF and LO signal sources can operate over a narrower frequency range than typical signal sources used with a VNA, and will be less expensive. Further minimizing costs, the wafer probe of the present invention preferably uses integrated circuits for frequency multiplication, upconversion, downconversion, and mixing manufactured for collision avoidance radar systems. Such integrated circuits will operate over the desired 76-77 GHz frequency range and will experience a reduction in cost as increased numbers of the collision avoidance radar systems are manufactured. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further details of the present invention are explained with the help of the attached drawings in 
     FIG. 1 shows typical components included in a VNA; 
     FIG. 2 shows components for the test set of FIG. 1; 
     FIG. 3 shows components for the RF modules of FIG. 1; 
     FIG. 4 shows components included in a wafer probe of the present invention; and 
     FIG. 5 shows a wafer probe with a layout for built in components of the RF module of FIG.  4 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 4 shows components built into one or more wafer probes of the present invention along with connections to components of a signal generator and test set provided separate from the wafer probes. The wafer probes of the present invention can each include built in components for one of the RF modules  401 - 402 . The need for RF modules provided separate from wafer probes used with a VNA, such as RF modules  104  and  105  illustrated with respect to FIG. 1 is, thus, eliminated. 
     The RF modules  401 - 402  receive an RF signal from a separate RF signal source  410 , similar to the RF signal source  101  of FIG.  1 . The RF signal source  410  is designed to operate over a 19.125±0.5 GHz range which will be multiplied up to a 74.5-78.5 GHz range in the RF modules  401 - 402  to enable testing throughout the 76-77 GHz collision avoidance radar bandwidth. With only a 19.125±0.5 GHz output signal required, a lower cost device can be used for the RF signal source  410  than a broadband device typically providing a 2-20 GHz, such as the Anritsu 68037B signal source as discussed previously. The output of the RF signal source  410  is provided to the RF modules  401 - 402  through a transfer switch  414  of a test set, similar to transfer switch  202  of FIG.  2 . 
     The RF modules  401 - 402  further receive a LO signal from a separate LO signal source  416 , similar to the LO signal source  100  of FIG.  1 . The LO signal source  416  is designed to operate over a 19.125±0.5 GHz range which will be multiplied up to a 74.5-78.5 GHz range in the RF modules  401 - 402  for mixing with the RF signals with the signal frequency adjusted by a VNA controller to create an IF signal, such as the 270 MHz IF signal described earlier. With only a 19.125±0.5 GHz output signal required, a lower cost device can be used for the LO signal source  416  than a broadband 2-20 GHz device typically used. The output of the LO signal source  416  is provided to the RF modules  401 - 402  through a power divider  418  of a test set, similar to power divider  202  of FIG.  2 . 
     The RF modules  401 - 402  include the same components, so a description of the components of the RF modules  401 - 402  will be made only with respect to RF module  401 . In RF module  401 , an RF signal from the transfer switch is received by a circuit  420  labeled OSC40. The OSC40 circuit  420  includes a frequency multiplier  422 , and buffers  421  and  423  integrated onto a single circuit. The frequency multiplier  422  multiplies the 19.125±0.5 GHz signal by two to provide an output in the range of 38.25±1 GHz. An example of the OSC40 circuit which is commercially available is the CHV1040 Multifunction:K-band Oscillator and Q-band Multiplier manufactured by united monolithic semiconductors S.A.S. 
     The output signal from the OSC circuit  420  is provided to a circuit  425  labeled MFC3776. The MFC3776 circuit  425  includes a frequency multiplier  427 , and buffers  426  and  428  integrated onto a single circuit. The frequency multiplier  427  multiplies the 38.25±1 GHz signal from the OSC40 circuit  420  by two to provide an output in the range of 76.5±2 GHz. An example of the MFC3776 circuit which is commercially available is the CHU2077 W-band Multifunction MultiplieriMPA manufactured by united monolithic semiconductors S.A.S. 
     The output of the MFC3776 circuit  425  is provided through couplers  430  and  432  to the test port which is connected to a wafer probe contact. The couplers  430  and  432  are formed on a substrate as a microstrip circuit using conventional chemical vapor deposition and etching procedures. The coupler  430  serves to couple the output signal from the MFC3776 circuit  425  as an incident reference signal to a mixer circuit  434 . The coupler  432  serves to couple a signal received at the test port as a test signal to the mixer circuit  436 . 
     To provide a LO signal to the mixer circuits  434  and  436 , a power divider  437  provides the LO signal from power divider  418  to OSC40 circuits  438  and  439 . The power divider  437  is formed on a substrate as a microstrip circuit using conventional chemical vapor deposition and etching techniques. 
     The OSC40 circuits  438 - 439  each include the same components as the OSC40 circuit  420  and serve to multiply the 19.25±0.5 LO signal by two to provide a 38.25±1 GHz output. The output of the OSC40 circuits  438  and  439  are provided to the inputs of respective MCF3776 circuits  440  and  441 . The MCF3776 circuits  440 - 441  each include the same components as the MCF3776 circuit  425  and serve to multiply the 38.25±1 GHz signal by two to provide a 76.5±2 GHz output to the LO inputs of respective mixers  434  and  436 . 
     The mixer  434  serves to mix the reference RF signal with the LO signal from the circuit  440  to provide a reference IF signal (REF IF). The REF IF signal can then be provided from a wafer probe to a test set, such as  102  of FIG. 1, and then from the test set to a VNA controller, such as  108  of FIG.  1 . The mixer  436  serves to mix the test RF signal with the LO signal from the circuit  441  to provide a test IF signal (TEST IF). The TEST IF signal can also be provided from the wafer probe through a test set to a VNA controller. An example of an integrated circuit for either of the mixers  434  and  436  is the W-band Double Mixer manufactured by united monolithic semiconductors S.A.S. 
     As in FIG. 1, the VNA controller such as the Anritsu 3735A can be used to provide a signal over a GPIB to control the frequency of the RF signal source  410  and the LO signal source  416 . The LO signal source frequency is offset from the RF signal source frequency to provide a test signal in the range of 270 MHz. Although not shown, the VNA controller can also provide signals over a GPIB to a PCB assembly of a test set, such as the PCB assembly  206  of FIG. 2, to control a voltage level provided to the amplifying buffers of the OSC40 and MCF3776 circuits to control amplifier gain. 
     FIG. 5 shows a layout of components of the RF module  401  of FIG. 4 built into a wafer probe. The wafer probe includes a housing  501 . The housing supports a probe tip  502  which is contacted to circuits on a wafer to enable testing the wafer. The RF module  401  is placed on a substrate which is supported by the housing  501 . With integrated circuit components used which are manufactured by united monolithic semiconductors S.A.S., as described above, the RF module  401  can occupy an area as small as of 0.617 in by 0.690 in., enabling the RF module  401  to be included on the wafer probe instead of on a device separate from the wafer probe. The test port of the RF module  401  as provided from coupler  432  provides a signal to the probe tip  502 . A cable  504  connects the OSC40 circuit  420  to a test set to receive the output of a RF signal source. A cable  506  connects the power divider  437  to a test set to receive the output of a LO signal source. Additional cables or wiring (not shown) will be further connected to the RF module  401  to provide +12V and +15V DC signals to amplifiers. 
     Although the present invention has been described above with particularity, this was merely to teach one of ordinary skill in the art how to make and use the invention. Many other modifications will fall within the scope of the invention, as that scope is defined by the claims provided below. For example, with further development of collision avoidance radar systems, new components may be available to perform upconverting, downconverting, and mixing performed by the components shown in FIG. 4 making up RF module  401 . For instance, components from the OSC40 and MFC3776 circuits may be combined onto a single chip. Further, the mixers  434  and  436  may be combined with frequency multipliers from the OSC40 and MFC3776 chips onto a single chip. Use of such chips, or only a portion of such chips, is believed within the scope of the present invention.