How to create a higher voltage AFE for a 1Mhz ultrasonic transducer - Page 1
Forum section: electronics / projects

author: pcarew
author_rank: Contributor
timestamp: May 16, 2025, 05:48:33 pm
content: Hello I have a design is for a battery/energy harvested water flow meter using the TDC1000 Ultrasonic chipset(https://www.ti.com/product/TDC1000).I have the design working through glass containers holding water, but when I use PVC pipes with water, the signal is too weak.The TDC1000 is running at 3.3v which is what is being applied to the ultrasonic 1Mhz transducer.My thought is to use a boost converter to boost the 3.3v up to a higher transducer voltage (up into the ~ 30v or so range).These transducers are rated for voltages up to ~100volts.The TDC1000 reference design (see attached image) has the Transmit pinstiedto the Rx pins, as the chip switches between transmit and receive modes for a transducer automatically.However, the TDC1000 electrical spec says that any voltage more than VDD+.6 on a pin will damage the chip, so obviously I can't have the upped voltage appear on the Rx pin.So, I was wondering if anyone could suggest some circuit ideas, where the Tx pin drives a Mosfet switch, to apply the "stepped up" higher voltages to the transducer, but the receive pin has that voltage 'clipped' to VDD.Any suggestion of an analog circuit to effect the higher voltage FE for the TDC1000?ThanksPaul

author: David Hess
author_rank: Super Contributor
timestamp: May 16, 2025, 06:07:25 pm
content: Why not clamp the signal to Vdd and Gnd with schottky diodes?

author: pcarew
author_rank: Contributor
timestamp: May 16, 2025, 06:13:18 pm
content: Hello David,Thanks for replying. I'm not sure I can visualize this arrangement.If I tied a diode between the Rx pin and ground, that would clip the rx pin voltage, but would it not also clip the voltage at the transducer when the chip is in TX mode?Paul.

author: voltsandjolts
author_rank: Unknown
timestamp: May 16, 2025, 06:19:31 pm
content: I think what you want is a piezo tx/rx switch, like say theMicrochip MD0100, or similar.

author: pcarew
author_rank: Contributor
timestamp: May 16, 2025, 06:35:05 pm
content: Thank you 'VoltsandJolts', I'll investigate. This sounds like an interesting device.Paul

author: David Hess
author_rank: Super Contributor
timestamp: May 16, 2025, 06:41:22 pm
content: Quote from: pcarew on May 16, 2025, 06:13:18 pmIt would only clip the transmit through the coupling capacitors.

author: pcarew
author_rank: Contributor
timestamp: May 16, 2025, 07:17:33 pm
content: Thanks David,I'll investigate with a breadboard

author: coppercone2
author_rank: Super Contributor
timestamp: May 16, 2025, 08:58:58 pm
content: the way that schematic is drawn it reminds me of a instrument like a tuba

author: moffy
author_rank: Super Contributor
timestamp: May 16, 2025, 11:47:19 pm
content: Quote from: voltsandjolts on May 16, 2025, 06:19:31 pmThe MD100 can protect the Rx input, but at 1MHz to advise on a HV amplifier it would be necessary to first know the load capacitance of the piezo transducer.

author: Niklas
author_rank: Frequent Contributor
timestamp: May 17, 2025, 06:49:11 am
content: Can you describe the interface between the transducer and the water pipe? What I am curious about is the potential losses or reflections in for instance an air gap. It is common to use a gel as an interface during ultrasound diagnostics in hospitals, as an example.Are you using more than just the transmitter and receiver functionality of the IC, or would it be possible to skip it and build the driver and receiver by yourself?

author: pcarew
author_rank: Contributor
timestamp: May 23, 2025, 09:03:57 pm
content: Hello Niklas,The transducer is "coupled" to a PVC water pipe with either acrylic rod or clear epoxy resin at a 30 degree angle. This transducer+coupling material is clamped to a 1 inch (2.54cm) PVC pipe with silicon gel between the mating surfaces.No Air gaps.There are two of these transducer setups, clamped to the pipe facing each other at a distance of approx 88mm (25.4/tan30deg)*2Paul.

author: pcarew
author_rank: Contributor
timestamp: May 23, 2025, 09:24:45 pm
content: Hello Moffy,QuoteGood question.I have been using two different Transduces, one Chinese and 1 from Germany.The Chinese one has the following specs:Code:1MHz ultrasonic transducer sensor1.Usage:Flow meter:2. Diameter:20mm;3. Frequency:1MHz;4. Bandwidth:0.2MHz;5. Echo Sensitivity(0dB=3Vp-p, 8Bursts,8cm):≥-30dB;6. Parallel Resistance:130Ω±30%;7. Capacitance:1200pF±20%;8. Input Voltage(Pulse):500Vp-p;9. Directivity(-3dB):7°±2°;10. Distance of Detection:0.1~5M;11.Pressure Resistance:1.5MPa;12.Operating temperature:0°C~+95°C;The German one is from:Code:Audiowell International LLCManufacturer Product Number: US0014-001The specs are:Code:Static Cap 1150 pFResonant Impedance <= 110Datasheet:https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/956/US00

author: moffy
author_rank: Super Contributor
timestamp: May 25, 2025, 12:51:25 am
content: So at 1MHz they have an impedance of roughly 100 Z , so you need a current booster to drive the load.https://www.analog.com/media/en/technical-documentation/application-notes/an18f.pdf

author: Niklas
author_rank: Frequent Contributor
timestamp: May 29, 2025, 07:25:06 am
content: To me it seems that the coupling path between the transducer and the liquid is too soft and will attenuate the impulse energy, so increasing both the output power and the input gain might work.On a previous job I designed a driver and receiver for a 1 MHz piezo transducer application to measure properties of a water based liquid. In an older generation, the pizeo element was placed inside a stainless steel cup with a wall thickness of slightly less than 1 mm with a droplet of acoustic gel in the front and a rubber plug as backing. A 2 mm steel plate located approx 80 mm away was used as a reflector. The transduced was excitated by a burst of 1 MHz pulses with approx 15 V amplitude and the received echo was roughly the same amount of mV so it needed a lot of amplification.For the newer generation we got a new transducer which was a sandwich constrution with both a hard front plate and tungsten filled backing. It was glued to the inside of a very hard plastic housing, with a wall thickness of less than 1 mm, using a thin layer of heat curing glue sheet. Due to the better transducer construction and the introduction of an inductive series matching, the received amplitude was in the range of 10-20% of the transmitted amplitude.Piezo driver supply voltageStart by using an adjustable power supply to establish the needed output voltage.Piezo driverI used bipolar transistors BC546 and BC556 in a push-pull configuration together with some capacitors for level shifting and to speed up the switching.V+ Supply voltageV- 0VInput, 3.3V logic signal, active low. Could be a burst of a few pulses.Rb, around 10k, in parallel with B-E on each transistor. No need for the additional deltaV. Add a Schottky BAT54 in reverse of the BE junction in each transistor.C, adjust based on the switching waveform with the selected transistors. Somewhere between 150pF and 1nF is a good starting point. Too little and the driver output will turn off before the end of each pulse.R in parallel with C, remove and place one series resistor from the logic input. 47 ohmsAdd Schottkys BAT54 for freewheeling on both transistor, similar to body diodes on MOSFETs.Adjust the values to achieve a square wave output.Series matchingWith 1 nF and 1 MHz, rewrite f=1/(2*Pi*sqrt(L*C)) to extract L. 22uH is a good starting point. Add a 10 ohm series resistor to lower the Q and to soften the peak currents through the driver transistors slightly. With a good matching, the voltage waveform over the piezo element will be close to a sine wave and with higher amplitude than your supply voltage. No need to fine tune the sine shape, opt for maximum amplitude. I got close to 45 V peak-peak when using 14 V as supply voltage.Piezo transducerConnect between the series matching and 0V.ReceiverA bandpass filter with suitable gain and possibly also some clamping of the input voltage. I used a combination of a high pass filter followed by a low pass filter, both second order multiple feedback. For clamping, add two Schottkys between 0V and the opamp's Vdd with the midpoint connected after the first input capacitor on the high pass filter. Be aware that the Schottkys will add a few pF of capacitance, especially when increasing the temperature above 35-40'C and this will affect the filter's transfer function. Might not be an issue if you only want to have a pulse for time of flight measurement. Make sure that the opamps are fast enough based on the needed gain, 100 MHz GPBW is a good start.