Abstract:
An electrical switching array and method uses a programmable multi-channel analog switch with a high voltage T/R switch and voltage limiting circuit for ultrasound image system echo signal multiplexing beamforming receiver frontend circuit.

Description:
RELATED APPLICATIONS 
     The present application claims the benefit to and is related herewith to U.S. Provisional Application entitled, “PROGRAMMABLE ECHO SIGNAL MULTIPLEXER WITH T/R SWITCH FOR ULTRASOUND BEAMFORMING INTEGRATED CIRCUIT AND METHOD”, filed May 24, 2010, and having U.S. Ser. No. 61/347,756 in the name of the same inventor, and which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to an ultrasound beamformer circuit and, more specifically, to a programmable multi-channel analog switch with a high voltage T/R switch and voltage limiting circuit for an ultrasound image system echo signal multiplexing beamforming receiver frontend circuit. 
     BACKGROUND OF THE INVENTION 
     Medical or nondestructive testing (NDT) ultrasound imaging applications have a growing demand for more sophisticated echo signal beamforming in the receiver frontend circuit. This may be necessary to generate high resolution acoustic images. The conventional ultrasound echo multiplexing circuits usually have an array of high-voltage analog switches (MUX) in between a transducer probe PZT array and multiple Tx/Rx channel circuitry. 
     These circuits have several limitations. These circuits first require Tx and Rx channel having an equal number of channels. Second, the transmitting pulses are generally high voltage and the receiving echo signals are generally low voltage. However, both signals have to pass through the same MUX. This requires that every MUX switch must have a low on-resistance when its turned on, and that it can withstand high voltage when it is turned off. These requirements make the cost of the MUX switch very high. 
     Therefore, it would be desirable to provide a circuit and method that overcomes the above problems. The circuit and method would be able to switch the echo signal only to overcome the above problems. 
     SUMMARY 
     In accordance with one embodiment, an electrical switching array circuit has at least one switching circuit. A control interface is coupled to the at least one switching circuit to activate and deactivate the at least one switching circuit. A high-voltage Transmit/Receive (T/R) switch is coupled to the at least one switching circuit. A clamping circuit is coupled to the at least one switching circuit and the high-voltage T/R switch. 
     In accordance with one embodiment, a protection circuit for a switch array circuit has a programmable on/off control digital interface. A high-voltage transmit/receive (T/R) switch is connected at an input terminal of the switch array circuit. A voltage limiting circuit is connected to the input terminal of the switch array circuit. 
     The present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a prior art schematic diagram illustrating a conventional high voltage (HV) analog multiplexer for an ultrasound image system with 64-channel of transmit/receive (Tx/Rx) and 192-element array probe transducer; 
         FIG. 2  is a schematic diagram illustrating a low voltage analog switch array with diode clamping and high voltage T/R switches accordance with one embodiment of the present invention; and 
         FIG. 3  is a schematic diagram illustrating a low voltage analog switch with additional output damping switch. 
     
    
    
     Common reference numerals are used throughout the drawings and detailed description to indicate like elements. 
     DETAILED DESCRIPTION 
     In the present invention, a digital programmable, low voltage analog switch, diode voltage clamping circuit and high voltage T/R switch circuit provides an ultrasound imaging system an echo receiving frontend suitable for large number array transducer elements of electronics controlled dynamic focus, acoustic phase-array, and receiving beamforming technology, which may be used in color Doppler image portable ultrasound machines. In various embodiments, the digital programmable, low voltage analog switch, diode voltage clamping circuit and high voltage T/R switch circuit channels are integrated into very small ICs. 
     Referring to  FIG. 1 , an ultrasound image system  100  of the prior art is shown. The schematic diagram of the ultrasound image system  100  illustrates a conventional high voltage analog switch multiplexer with 64-channel of Tx/Rx and 192-element array probe transducer. 
     In operation, the multiple channels of Tx pulser  101  send bipolar or unipolar high voltage excitation pulses, through high voltage T/R switches  106  and multiplexing switch  113 , to the PZT-array probe transducers  105 . The Tx pulses peak to peak voltage may be between anywhere from +/−2V to +/−150V. The low voltage echo signals received by the same or different PZT elements  105 , then through the switches  113  and  106  back into the receiver channel LNA  112  and ADC  115 . 
     Usually the peak to peak voltage of the echo signal is only about +/−0.8V to as small as few micro-volts. The echo signals then being processed by the digital rear side FPGA interface  116 , CPU  118  and data memory  117  then through video circuit send to display  120  and an acoustic image. This is the prior arts of conventional ultrasound image system architecture of configuration. 
     Referring now to  FIG. 2 , a schematic block diagram illustrating an ultrasound image system  200  is shown. The ultrasound image system  200  has a plurality of low-voltage receive beamforming analog switch circuits  209  (hereinafter low voltage switches  209 ). The low voltage switches  209  may be comprised of a pair of MOSFET transistors  209 A and  209 B. The input of each of the low voltage switches  209  is connected to a respective clamping circuit  207  and to a respective output of a T/R switch  206 . In accordance with one embodiment, the clamping circuit  207  is comprised of a pair of diodes  207 A and  207 B. 
     The outputs of the low voltage switches  209  are selectively connected through package lead  211  to a Low Noise Amplifiers (LNA)  212 . A serial digital or serial peripheral interface (SPI) circuit  213  is coupled to each of the low voltage switches  209  and provides programmable means to control the low voltage switches  209 . 
     A plurality of transmit (Tx) pulser  201  is each powered by VPP and VNN high voltage supplies  202  and  203 . The output of each of the Tx pulsers  201  are coupled through isolation diodes  204  and an impedance-matching resistor  215 , connected to an array PZT element  205 . The array PZT element  205  is also connected to the input of the array of high voltage T/R switches  209 . 
     The T/R switch  206  is a two-terminal voltage controlled normally-on switch. During the high voltage Tx pulse  201  existing period, the T/R switch  206  is off or in very high impedance state. The diodes back-to-back clamping circuit  207  provides LV switch input voltage limits against any leakage of the T/R switch  206 . It makes sure the input of the low voltage switch  209  will always be within about a peak-to-peak diode drop, which usually is in the range of approximately +/−0.5 to +/−1.2V of the voltages. The useful echo signals usually are only few hundred mV to μV range. Therefore, the array of the low voltage switches  209  only needs work at a very low input voltages range. 
     A MOSFET “T” switch  210  is connected to a middle point of the main MOSFET switch  209 B of the low voltage switch  209 , to increase the off-isolation of the low voltage switch  209  in a high-frequency (RE) range. When the main MOSFET switches in the low voltage switch  209  are turned on, the “T” switch  210  is off, when the low voltage switch  209  is off the switch  210  will be on. 
     All low voltage switches  209  are controlled by the outputs of a serial register Q0˜Qn in  213 . 
     Referring to  FIG. 3 , an additional analog switch  314  is connected to the output of the low voltage switch  209  and to ground. The additional analog switch  314  may be used to provide additional low impedance damping path for the output and LNA input circuits  312 , on each channel  311 . 
     This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process, may be implemented by one skilled in the art in view of this disclosure.