Texas Instruments (TI) recently introduced TUSS4440 and TUSS4470 which are extending TI’s existing portfolio of ultrasonic sensing ICs for time-of-flight applications. Both are analog frontend ICs (“AFE”) for driving sound transducers and a receiver stage for echo sensing. Alternate IC solutions by TI, Maxim, Elmos, TDK (Chirp) are available. How do they differentiate?
How it works
In general, with ultrasound sensors you can detect presence of objects and measure the distance to an object using time-of-flight (ToF) – in a range of few centimetres up to several meters. For this purpose, the sensor (also called “transducer”) emits a pulsed signal (burst) at the speed of sound which is echoed by objects in the sensor’s field-of-view. Measured round trip time corresponds to the distance of the object. Watch this video as a starting point.
Target Applications
To measure the distance to an object or its shape are standard use cases for ultrasonic sensing ICs for time-of-flight. But you can also measure material thickness or concentration or identify an object by sensing its surface. Another application area are moving objects. For example, you can detect changes to an environment, e.g. the entrance of an object to a room. Or you can track object movement or monitor the distance of two objects or a range.
Looking at different target market sectors, this is a collection of possible applications:
- Automotive, Transport: assistance and safety functions, e.g. to avoid collisions. Pedestrian detection, car parking assistant, altimeter for drones.
- Industrial, Robotics, Logistics: measure fill heights, people counting, cleaning robot obstacle detection, identification of objects, automatic door opening, parcel size measurement, surveillance systems, quality control
- Human-machine interfaces and gaming: track movements of humans for video games or detection of gestures for control of equipment
- Smartphones: distance information for example can be used to improve the quality of photos by providing the camera software with information about foreground and background.
Usually, ToF is using light as a carrier for the burst stimulus, typically infrared (IR) light. For IR-based ToF there are many chip manufacturers offering solutions, e.g. Infineon, Melexis, STMicroelectronics and Texas Instruments.
For IR-ToF already 100+ mio chips p.a. are being shipped today, and volumes will certainly continue to grow (see more info in ref. 3), esp. if ToF solutions succeed to extend presence in consumer applications. So, into which market segment the ultrasonic alternative will go?
For sure, ultrasound sensing offers some natural advantages (vs. optical sensing) with transparent or dark objects or liquids which will not stop sound waves from bouncing back, where light does not reflect properly. In addition, ultrasound sensors will also work in sunlight or smoky environments or gas.
Texas Instruments is offering both kind of ToF solutions, a fact which is granting some extra credibility to TI’s view of related pros and cons. TI points out that ultrasonic ToF is facing difficulties with soft target objects (e.g. sheeps) because part of the ultrasonic energy is being absorbed rather than reflected by them. And, by nature, ultrasonic sensing solutions will be slower because light is faster than sound… Besides that, TI is promoting their ultrasonic sensing ICs for time-of-flight as their “lowest cost proximity solution”.
System Overview
An ultrasonic sensing system for time-of-flight consists of several building blocks. Depending on target application, some elements require careful selection or adjustment for best results.
Figure 1: System Block Diagram for ultrasonic time-of-flight sensing (© chip-info.com)
Usually, the ultrasonic sensor (*) is a piezoelectric transducer which works both ways, i.e. as a loudspeaker and a microphone – at the same single frequency. TI points out that selection of an appropriate transducer is a key factor for the overall performance of the system (one or two separate transducers, closed top or open top, field of view, etc.). Pulse generation (frequency, pulse count) is another important parameter to be tailored to target application requirements regarding detection range or to transmission medium (air, liquid, etc.)
In general, the system has to listen for return echoes from objects in the sensor’s field of view. The receiver part has to filter incoming signal, remove noise and gain it up before it can be forwarded to an ADC for digitisation. Then, a digital signal processor (DSP) or an MCU will perform further processing to exclude “trash” and focus on extraction of useful time-of-flight data from objects of interest.
Texas Instruments TUS4440/70
TI’s new TUSS4440/70 features an integrated driver incl. pulse generator and the Analog Frontend (AFE), see Figure 1. All other functional blocks must be implemented separately.
The TUSS4470 integrates an H-bridge to drive the transducer directly. This is useful in applications where the receive transducer sensitivity is high, large driving voltage is not required or where short distance measurements are needed. TUSS4440 is a transformer drive analog front end for industrial ultrasonic applications requiring more sound pressure. Both can support a single transducer to send and receive burst signals, or can set up two transducers to split the send and receive functions.
The AFE contains receives and conditions the echo signal from the transducer during listen mode. The implemented analog process (principle see Figure 2) is extracting an echo envelope which can be fed to the next stage (external): an A/D-converter resp. to the ADC input of a microcontroller.
Figure 2: Extraction of analog echo envelope (© chip-info.com)
The received echo is first amplified with a fixed linear low-noise amplifier, followed by a bandpass filter to remove noise out of the expected signal band. Then a logarithmic amplifier plus low-pass filter is extracting the signal which is buffered to the OUT3 pin.
Figure 3: TUSS4440/70 Analog Frontend Receiver (© chip-info.com)
The bandpass filter is critical for reducing noise to allow utilization of the complete dynamic range of the logarithmic amplifier. Therefore TUSS4440/70 allows a factory-trim to compensate variations of the chosen sensor and match sensor and AFE individually. This can be done individually by configuration to adjust the center frequency of the bandpass filter to be close the transducer frequency.
The logamp provides compression for large signal inputs and amplifies linearly small signal inputs. Logamp simplifies system design to detect varying strengths of echoes that happens because of difference in reflectivity of different types of objects and objects at different distances. It automatically adjusts its gain based on the input signal level. The output of the logamp is filtered using a low-pass filter to remove the high-frequency components and provide a sufficient peak hold time for the demodulated envelope signal.
In addition, an echo interrupt signal is triggered whenever the envelope reaches a user-configurable threshold. It can be used as an indicator that an object has been detected. A zero-crossing output is derived from the raw echo input signal and can be used to validate the frequency in order to increase robustness or to detect echo deviations.
Ti is offering a demo board called BOOST-TUSS4470 which (in combination with a suitable MSP430 MCU or own choice of host MCU) can be used to evaluate the TUSS4470. The associated TUSS Generation III EVM GUI can be used to customize, configure and control the ultrasonic setup, and to monitor the performance of the resulting ultrasonic activity.
For support purposes TI offers a dedicated discussion board (“e2e Community”) for sensors, also covering ultrasonic sensing ICs and applications. You also find some FAQs there.
Competition
Besides TI only few IC manufacturers are offering ultrasonic sensing ICs for time-of-flight: Maxim, Elmos, Chirp. It turns out that – besides electrical characteristics, packaging, cost, etc, – integration and flexibility are significant differentiators.
Texas Instruments PGA460
The new TUS4440/70 is challenging an in-house product which is available from TI since 2017: PGA460 Ultrasonic signal processor and transducer driver. The PGA460 is integrating a complete ultrasonic ToF subsystem incl. ADC and DSP (recall Figure 1).
TI is offering many design support instruments for PGA460: 2 evaluation boards (with and without sample transducer), software libraries, a reference design and an IBIS simulation model. In addition, a PGA460 library for Energia IDE incl. source code is offered which is aiming at TI’s MSP430, but probably a good starting point also for other host MCUs.
So, which TI product to select for your project?
- For an automotive application PGA460 might be unrivalled because an AEC-Q100 qualified PGA460-Q1 is offered.
- Also for straight-forward distance and proximity measurement TI recommends PGA460.
- And PGA460 costs less than TUSS4440 or TUSS4470 (PGA460: 1.95USD@1ku. TUSS4470: 2.99USD@1ku. Source: TI website on Feb 4, 2020)
- But for measurement of fill levels through liquid or concentration in liquids incl. identification of material TUSS4470 is recommended because a tailored transducer might be required, and TUSS4470 supports the widest range of transducer frequencies from 30kHz to 1Mhz.
- For measurement through solid material the TUSS4440 transformer driver might be required for a transducer to create sufficiently large sound pressure.
- For tracking of moving objects you can take advantage of TUSS4470 which supports cascading by independent usage of receive and driver paths of each chip.
- Also for surveillance applications (i.e. detection of environment changes) TUSS4470 is recommended because users can benefit from its unique “zero-crossing” feature.
Maxim
Maxim is offering a couple of devices aiming at flow meter applications for gas and liquids: MAX35101, MAX35103 and MAX35104.
MAXQ7667 is a complete system-on-chip for “time-of-flight ultrasonic distance-measuring” incl. ADC, DSP and a MAXQ20 microcontroller for control. The chip is expensive (10.29USD@1ku. Source: Maxim Website on Feb 4, 2020) and latest revision 1 of product datasheet is dated 07/2009, so it might not be recommended for new designs any more.
In general, Maxim offers an online Support Center incl. regional phone support and the option to submit an online support request (case), but no discussion board (forum).
Elmos
Elmos Semiconductor is offering a couple of AFEs similar to TI’s TUSS4440/70, see here. Elmos claims that these ICs “build the core for a robust and easy-to-handle distance measurement system, while offering flexibility for customer applications”. Also demo boards are offered.
For all products only 2-page product overviews are available for download, no further technical data or price info or support services are offered online.
Chirp CH-101
California-based startup company Chirp Microsystems (which is now InvenSense and part of TDK group) has created some attention when they introduced the CH-101 (see ref. 2 and 3). The CH-101 is a complete ultrasonic Time-of- Flight (ToF) system-on-chip including a patented MEMS transducer(!) in a single 3.5 x 3.5 x 1.26mm LGA package. The SoC runs Chirp’s DSP algorithms and includes an integrated microcontroller providing result data via I2C.
The CH-101 works in a range from 4 cm to 1,2 m and consumes 15μA max. during operation (1 sample per sec). An evaluation board is available as well as a Developers Corner which claims to provide all the tools needed for application development – after registration. This is where “developers gain access to our Software Downloads, Developers kits, Knowledgebase Center, Discussion Form, Application Pages, Support Center and eNewsletter”.
Conclusion
TI‘s ultrasonic sensing ICs for time-of-flight are able to address a wide range of target applications – at reasonable (hardware) cost. TI’s evaluation and reference boards plus software in combination with a well-established e2e Community are important ingredients for small- and medium- scale projects and customers.
Maxim might be a good alternative for industrial flow meters, Elmos for automotive applications like car parking assistance. With its small package size and lowest power consumption Chirp‘s CH101 is a candidate for handheld devices like smartphones.
References
- Texas Instruments website: www.ti.com
- EDN Magazine: “MEMS ultrasonic time-of-flight innovation: sensors advance user experiences”, December 2017
- EE Times: “Chirp Adds Sonar-on-Chip to ToF Battle”, December 2017
- other online references (URLs) are embedded in text
