Class-D Audio Amplifiers Target the Smart Home

Texas Instruments (TI) has introduced three new digital-input Class-D audio amplifiers that enable engineers to deliver high-resolution audio in more smart-home and voice-enabled applications. By combining first-of-its-kind integration, real-time protection and new modulation schemes, TI’s new audio devices allow designers to reduce board space and overall bill of material (BOM) cost. These new amplifiers are designed for personal electronics applications with any power level, including smart speakers, sound bars, TVs, notebooks, projectors and Internet-of-Things (IoT) applications.

TAS2770 15-W audio amplifier: Claimed by TI to be the first wide-supply I/V sense amplifier, the TAS2770 (shown) offers state-of-the art, real-time speaker protection when paired with TI Smart Amp algorithms. The amplifier monitors loudspeaker behavior and increases loudness while improving audio quality in applications requiring small speakers. The TAS2770 is an audio front end (AFE) that combines a digital microphone input with a powerful I/V sense amplifier. The device captures voice and ambient acoustic information for echo cancellation or noise reduction in voice-enabled applications. The TAS2770 monitors battery voltage and automatically decreases gain when audio signals exceed a set threshold, helping designers avoid clipping and extend playback time through end-of-charge battery conditions without degrading sound quality.

TAS5825M audio amplifier: Designers can achieve high-resolution audio with minimal engineering effort due to the device’s 192-kHz input sampling frequency and flexible, integrated processing flows. Additionally, the TAS5825M provides bass enhancement and thermal protection for the speaker. The TAS5825M’s dedicated serial audio interface data output provides ambient sound information to the applications processor. Engineers can reduce idle-power losses and thermal dissipation without degrading sound quality with the TAS5825M’s proprietary hybrid-mode modulation scheme.

TAS3251 audio amplifier: TI says the TAS3251 is the first integrated digital-input solution to support the highest output power and performance at 2x 175 W, all in one single package. You can enable up to 96-kHz flexible processing and self-protection features including cycle-by-cycle current limit and DC speaker protection with the TAS3251.

Designers can use TI’s PurePath Console software to easily configure the TAS2770, TAS5825M and TAS3251 Class-D audio amplifiers. Engineers can jump-start their design with the TAS2770 Stereo Audio Subsystem Reference Design. Additional resources and reference designs are available to help engineers with their smart speaker designs.

The TAS2770 Class-D audio amplifier is now available in volume quantities through the TI store and authorized distributors. Additionally, preproduction samples of the TAS5825M are now available through the TI store. The TAS3251EVM evaluation module is available today through the TI store and authorized distributors, and production quantities of the TAS3251 amplifier will be available in 2Q 2018.

Texas Instruments | www.ti.com

Wireless Data Links (Part 2): Transmitters and Antennas

If you built your own ham radio “back in the day,” you’ll recall the frustration of putting it together with components that were basic at best.

But as columnist George Novacek points out in the second installment of his series examining wireless data links: “Today you can purchase excellent, reasonably priced low-power gear for data communications off the shelf.”

Transmitter and receiver

Photo 1: SparkFun Electronics’s WRL-10524 transmitter and WRL-10532 receiver are low cost, basic, and work well.

Part 2 of Novacek’s series, appearing in the March issue, looks at transmitters and antennas.

In one section, Novacek expands upon the five basic data-transmitter modules—a data encoder, a modulator, a carrier frequency generator, an RF output amplifier, and an antenna:

Low-power data transmitters often integrate the modulator, the carrier frequency generator, and the amplifier into one circuit. A single transistor can do the job. I’ll discuss antennas later. When a transmitter and a receiver are combined into one unit, it’s called a transceiver.

Modulation may not be needed in some simple applications where the mere presence of a carrier is detected to initiate an action. A simple push button will suffice, but this is rarely used as it is subject to false triggering by other transmitters working in the area in the same frequency band.

Digital encoder and decoder ICs are available for simple devices (e.g., garage door openers) or keyless entry where just an on or off output is required from the receiver. These ICs generate a data packet for transmission. If the received packet matches the data stored in the decoder, an action is initiated. Typical examples include Holtek Semiconductor HT12E encoders and HT12D decoders and Freescale Semiconductor MC145026, MC145027, and MC145028 encoder and decoder pairs. For data communications a similar but more advanced scheme is used. I’ll address this when I discuss receivers (coming up in Part 3 of this series).

Novacek’s column goes on to explain modulation types, including OOK and ASK modulation:

OOK modulation is achieved by feeding the Data In line with a 0-to+V-level  datastream. ASK modulation can be achieved by the data varying the transistor biasing to swing the RF output between 100% and typically 30% to 50% amplitude. I prefer to add a separate modulator.

The advantage of ASK as opposed to OOK modulation is that the carrier is always present, thus the receiver is not required to repeatedly synchronize to it. Different manufacturers’ specifications claim substantially higher achievable data rates with ASK rather than OOK.

For instance, Photo 1 shows a SparkFun Electronics WRL-10534 transmitter and a WRL-10532 receiver set for 433.9 MHz (a 315-MHz set is also available), which costs less than $10. It is a bare-bones design, but it works well. When you build supporting circuits around it you can get excellent results. The set is a good starting point for experimentation.

The article also includes tips on a transceiver you can purchase to save time in developing ancillary circuits (XBee), while noting a variety of transceiver, receiver, and transmitter modules are available from manufacturers such as Maxim Integrated, Micrel, and RF Monolithics (RFM).  In addition, the article discusses design and optimization of the three forms of antennas: a straight conductor (monopole), a coil (helical), and a loop.

“These can be external, internal, or even etched onto the PCB (e.g., keyless entry fobs) to minimize the size,” Novacek says.

Do you need advice on what to consider when choosing an antenna for your design?  Find these tips and more in Novacek’s March issue article.

Dual-Channel Waveform Generators

B&K Precision 4053 Waveform Generator

B&K Precision 4053 Waveform Generator

The 4050 Series is a new line of four dual-channel function/arbitrary waveform generators. The instruments can generate 5-to-50-MHz waveforms for applications requiring stable and precise sine, square, triangle, and pulse waveforms with modulation and arbitrary waveform capabilities.

All models provide a main output voltage that can be vary from 0 to 10 VPP into 50 Ω and a secondary output that can vary from 0 to 3 VPP into 50 Ω. The generators feature a 3.5” color LCD, a rotary control knob, and a numeric keypad with dedicated waveform keys and output buttons.

The 4050 Series provides users with 48 built-in arbitrary waveforms. Using the included waveform editing software via the standard USB interface on the rear, users can create and load up to 10 custom 16-kpt waveforms. For general-purpose interface bus (GPIB) connectivity, an optional USB-to-GPIB adapter is available.

The generators offer a variety of modulation schemes for modulated signal applications including amplitude and frequency modulation (AM/FM), double sideband amplitude modulation (DSB-AM), amplitude and frequency shift keying (ASK/FSK), phase modulation (PM), and pulse-width modulation (PWM). Additional standard features include a linear and logarithmic sweep function, a built-in counter, sync output, a trigger I/O terminal, and a USB host port on the front panel to save and recall instrument settings and waveforms. A standard external 10-MHz reference clock input is provided to synchronize the instrument to another generator.

The 4052 (5-MHz) costs $499, the 4053 (10 MHz) costs $599, the 4054 (25 MHz) costs $850, and the 4055 (50 MHz) costs $1,050. Note: B&K Precision is offering 10% off MSRP through November 30, 2013. See website for details.

B&K Precision Corp.
www.bkprecision.com