Supertex inc. MD2134DB1 MD2134 Ultrasound Beamforming Transmitter Demoboard Introduction General Description The MD2134 is a high-speed, arbitrary waveform, push-pull This demoboard datasheet describes how to use the MD- source-driver. It is designed for medical ultrasound imaging 2134DB1 to generate the ultrasound transmit beam forming and HIFU beam forming applications. It also can be used in waveform with the Gaussian profile, and the adjustable fre- NDT, sonar and other ultrasound phase-array focusing beam- quency, amplitude and phase angle. It also provides informa- forming applications. tion about how to design a user application circuit and PCB using the MD2134K7 and DN2625DK6 devices. The integrated circuit (IC) consists of the CMOS digital logic input circuits, an 8-bit current DAC for the waveform amplitude The MD2134DB1 circuit uses a pair of depletion mode, high control, and four pre-stored Sine waveforms with pulse- voltage, DN2625 MOSFETs in the push-pull mode to drive amplitude-modulation (PAM) current sources. These current the center-tap wide band ultrasound output transformer. sources are constructed with the high-speed current-switch The MOSFETs are in one 8-Lead DFN surface mount pack- array and SPI programmable LV 15:1 PAM level registers. age. The sources of the MOSFETs are directly driven by the The PAM level resolution of the waveform is 7-bit, 128-step MD2134s two outputs, whose maximum peak sinking current plus sign. There are four logic inputs M 3:0 as fast control is up to 3.3A. These current-source outputs are controlled by signals. They control the push-pull current-sources output the MD1234s internal current source switch array and the in- timing, frequency, cycle in the burst, as well as the current- put signals M 3:0 . level output. The 15 level registers, along with the DAC value, together can be written and read-back via a SPI serial interface. All of the MD2134s logic control signals are generated by two small CPLD-programmable logic circuits clocked by an on- The MD2134s output stage is designed to drive two depletion board 160MHz crystal oscillator. The on-board CPLD circuits mode high voltage Supertex DN2625 N-type MOSFETs as not only generate accurate timing for the high-speed PAM level the source drivers. The MOSFET drains are connected to control waveforms, but also the serial data and clock to set and a center-tap ultrasound frequency pulse transformer. The change the waveform amplitude DAC and waveform selection secondary winding of the transformer can connect to the registers. The external clock input can be used if the on-board ultrasound piezo or capacitive transducer via cable and with a oscillator is disabled. The external trigger input can be used to good impedance match. MD2134 has a high-speed 120MHz synchronize the burst waveforms launch timing. serial data interface that can quickly update the beam forming apodization between scans. There are five push buttons for enabling and selecting the out- put waveform selection (PAM), amplitude (DAC) and chip en- Demoboard Block Diagram +3.3V +2.5V JTAG +2.5V +5.0V +5.0V +3.3V VCC VCCIO EN T1 VLL VDD PA M1 EXTRG DN2625 1:1:1 EXTRG M3 JUMP M0 +70 to 100V XDCX M2 V PP EXCLK CPLD MD2134 SDI 1k SDO C7 220pF SCK CLKIN OSC CS LOAD LD DN2625 160MHz DIS PB GND RFB Phase Wave DAC Freq PWR Phase EN +5.0V+3.3V Ampl ENA Doc. DSDB-MD2134DB1 Supertex inc. A070114 www.supertex.comMD2134DB1 able (EN). The FREQ button is not being used for this revision very small inductive loads, ringing and even oscillations are of firmware. Four color LEDs indicate the power, chip enable, possible. The supply voltage bypass capacitors and the waveform selection, and DAC states. The MD2134DB1 output MOSFET gate de-coupling capacitors should be as close to waveform can be displayed by using an oscilloscope and the the pins as possible. The capacitors ground pin pads should high impedance probe at the TP13 test point. It also can use have low inductance, feed-through connections that are con- an SMA to BNC 50 coaxial cable connected directly to an os- nected directly to a solid ground plane. The VDD and VPP cilloscope, with an attenuation of 5:1 if R is 200. A cable can supplies can draw fast transient currents of up to 3.5A, so they 10 also be used to drive the users transducer directly. Jumper J4 should be provided with a low-impedance bypass capacitor can be used to select whether or not to connect the on-board at the chips pins. A ceramic capacitor of 0.1 to 1.0F may be equivalent-load, which is formed by a 220pF capacitor in paral- used. Minimize the trace length to the ground plane, and in- lel with a 1.0k resistor. sert a ferrite bead in the power supply lead to the capacitor to prevent resonance in the power supply lines. For applications Circuit Design & PCB Layout that are sensitive to jitter and noise and when using multiple The thermal pad at the bottom of the MD2134 package must MD2134 ICs, insert another ferrite bead between VDD and be connected to the VSUB pin on the PCB. The VSUB is con- decouple each chip supply separately. Pay particular attention nected to the ICs substrate. It is important to make sure that to minimizing trace lengths and using sufficient trace width to the VSUB is well grounded. A proper supply voltage power-up reduce inductance not only on the supply pins but also on the sequence is needed to test the circuit. To prevent any sup- CA/B and KA/B compensation pins. Very closely placed sur- ply voltage polarity reversing, the circuit also has protection face mount components are highly recommended. Be aware Schottky diodes (D7, D8 and D9). of the parasitic coupling from the high voltage outputs to the input signal terminals of MD2134. This feedback may cause Due to the high current and high current slew rate nature of oscillations or spurious waveform shapes on the edges of this common gate, source-driven and push-pull circuit topol- signal transitions. Since the input operates with signals down ogy, the two cascading N-channel MOSFETs need to have to 2.5V, even small coupling voltages may cause problems. very low lead inductance of the connections. The Supertex Use of a solid ground plane and good power and signal layout DN2625DK6 is designed for this application and works with practices will prevent this problem. Also ensure that the cir- the MD2134K7 seamlessly. In particular, a good PCB layout culating ground return current from a capacitive load cannot design needs to shorten the traces between the MD2134K7 react with common inductance to create noise voltages in the output pins and the DN2625DK6 source pins. It is also neces- input logic circuitry. sary to connect all three pairs of pins between them for the high current carrying capacity. Furthermore, because of the This MD2134DB1 demoboard should be powered up with high di/dt current in MD2134s outputs, it is also necessary to multiple DC power supplies with current limiting functions. The connect the Schottky diodes D5 and D6 from the driver output power supply voltages and current limits used in the testing pins connected to the +5.0V power supply line, as the clamp- are listed on page 7. There are examples of the MD2134DB1 ing diodes. Note that the diodes must have enough speed and demoboard input and output waveform and measurements peak current capability. The RC snubber circuits of R8-C5 and shown in Figures 1 to 7 below. R15-C28 at the output pins can dump the current pulse edge ringing effectively. Output Transformer Design The center tap, wide band, ultrasound transformer for push- PCB designers need to pay attention to some of the connect- pull output circuit serves three functions: a balanced-differen- ing traces as high-voltage and high-speed traces. In particular, tial to single-end output transformer an isolation barrier to the low capacitance to the ground plane and more trace spacing ultrasound probe and an impedance matching or low-pass needs to be applied in this situation. network combined with the cable and transducer element. The MD2134 PAM clock may operate at a 80 to 160MHz frequen- High-speed PCB trace design practices that are compatible cy range, however the wide band transformer needs only to with about 100 to 200 MHz operating speed are used for the work in the frequency band of the dummy load (220pF//1.0k). demoboard PCB layout. The internal circuitry of the MD2134 Besides the bandwidth consideration, the small transformer can operate at quite a high frequency, with the primary speed should be designed using a ferrite magnetic core selected to limitation being load capacitance. Because of this high speed give high enough saturation current and low leakage induc- and the high transient currents that result when driving even tance. Doc. DSDB-MD2134DB1 Supertex inc. A070114 2 www.supertex.com