Electronic Design

Digital TV, Audio Boost Analog/Mixed-Signal

Innovation in the analog domain has never been stronger thanks to a series of new applications from the digital side.

It's next to impossible to encapsulate the concept of "high-performance" analog in a few simple datasheet specs like bandwidth or conversion rate or resolution. Dimensions of performance, to borrow a term from Analog Devices, expand and contract according to the application, and they include less obvious factors like power consumption, package size, and even price.

One way to sort out performance issues is to sort new analog products by application area to see where they cluster and what specs are emphasized. If you do that, innovation and competition are clearly strongest in the multimedia market. In fact, many new analog products don't fit the traditional amplifier/data converter categories.

There are new competitors as well. Fairchild Semiconductor now has its own Korean fab and is making monolithic amplifiers for digital video. Cirrus Logic continues to redefine itself as a performance leader in high-end audio and digital TV. Meanwhile, the established analog players, including ADI, National Semiconductor, Linear, Intersil, Maxim, and Texas Instruments, continue to innovate.

Let's start with a look at new products for video that are destined for OEM products from cell phones to HDTV receivers. Fairchild Semiconductor's 210-MHz FHP3x50 family (triples and quads) and 50-MHz FHP3x30 family (single, dual, and quad) target high-definition (HD) and standard-definition (SD) video applications, respectively (Fig. 1).

The HD devices exhibit 210-MHz, −3-dB bandwidth, and 1100-V/µs slew rates, along with 0.07%/0.03° differential gain and phase errors. Their 0.1-dB gain flatness extends to 50 MHz. Both consume 3.6 mA of supply current per amplifier. Additionally, a ±55-mA output current rating supports multiple video loads.

The SD family is characterized by 16-MHz, 0.1-dB gain flatness, greater than 100-dB open loop gain, power-supply rejection ratio (PSRR), and common-mode rejection ratios (CMRRs). They draw 2.5-mA supply current per amplifier while providing ±100-mA output capability—enough to support four video loads. Thousand-piece unit pricing is $0.71 and $0.83 for the triple and quad HD parts and from $0.63 to $0.86 on the SD parts, depending on the number of amps and package type.

The LT6557 single-supply, triple video amplifier from Linear Technology fits high-resolution LCD projectors and monitors as well as automotive display systems (Fig. 2). Its input swing extends to 0.8 V of the rails, enabling it to amplify a full video signal when operating from one 5-V supply. Its 23-dB bandwidth is 500 MHz, slew rate is 2200 V/µs, and settling time is 4 ns. And, its 0.1-dB gain flatness extends to 120 MHz.

An internal biasing feature lets circuit designers program the inputs of all three amplifiers to the same dc voltage level with a single resistor. Pricing starts at $2.50 each in 1000-piece quantities.

Also for applications in projectors and monitors, National Semiconductor's LMH6582 (gain = 1) and LMH6583 (gain = 2) 16-by-8 analog crosspoint switches also achieve a 500-MHz, −3-dB bandwidth, with 0.1-dB gain flatness out to 100 MHz and slew rates up to 3000 V/µs. Channel-to-channel crosstalk is −50 dBc at 100 MHz. Each buffered output can drive up to two back-terminated, 75-Ω ½ video loads.

One of the really clever features of the chips is their pin arrangement Essentially, diagonal symmetry in pin assignments makes it easy to use direct pin-to-pin vias when the parts are mounted on opposite sides of a board. As a result, a pair of chips forms either a 16-by-16 crosspoint or a 32-by-8 crosspoint. Both devices cost $39.95 in 100-unit quantities.

National also introduced a low-jitter sync separator IC for high-definition video formats that eliminates the need for extra filtering and jitter-cleaning stages. The LMH1981 accepts video signals from composite (CVBS), S-video (Y/C), component (YPbPr), and computer interfaces, providing horizontal, vertical, and composite sync, odd/even field, and burst/back porch clamping.

It accepts both bi-and tri-level sync video inputs. Proper, 50% slicing ensures accurate separation of signals that vary in amplitude, offset, and noise. Based on National's inputreferred jitter testing of high-definition video inputs, horizontal-sync jitter can be as much as 30% lower than approaches that use multiple stages or FPGAs after sync separation to clean and filter jitter.

Automatic video-format detection can be used to inform the downstream video system of format changes so the system can dynamically adjust system parameters, such as color space or scalar conversions. An output pin on the chip outputs the total vertical resolution or line count through an 11-bit binary data stream.

The LMH1981 operates on single-supply voltages between 3.3 and 5 V. It's compatible with the Macrovision Video Copy Protection System commonly used in VHS and DVD video sources. Sampling now, the LMH1981 will cost $3.79 in 1000-unit lots.

Flat-panel TVs, which lack a place to put conventional speakers, are providing new opportunities for Class D audio power amps. For example, Cirrus Logic's CS44130 power stage IC comes with a reference design for stereo and 2.1-channel applications. Its thermally enhanced 9- by 9-mm quad flat no-lead (QFN) package eliminates the need for a heatsink. Nevertheless, it provides up to 60 W and is thermally and electrically self-protected. The outputs can be configured as four half-bridge channels, two full-bridge channels, or one parallel fullbridge channel. Because it operates Class D, efficiency is a high 90%.

The reference design includes Cirrus' CS44600 digital amplifier controller. Together, the CS44130 and CS44600 enable a high-power stereo amplifier in less than three square inches of pc-board space. The CS44600 incorporates patented power-supply rejection feedback technology, which enables the 44130's single-ended outputs. It also compensates for power-supply noise. In lots of 10,000, the CS44130 starts at $2.78. The CS44600 costs $2.98.

For high-end consumer and professional audio applications, Cirrus' CS3318 and CS3308 volume-control ICs offer eight audio channels to control 7.1 surroundsound. The CS3318 runs on 9 V, and the CS3308 runs on 5 V. They let consumers set nominal volume levels between ?96 and +22 dB in 0.25-dB steps while passing 127 dB of dynamic range for the CS3318 and 123 dB for the CS3308. Previously, the finest granularity for digital volume control was 0.5 dB.

Other features include dynamic address assignment and simultaneous master volume controls across devices via a single serial control bus, such as I2C or SPI. The chips cost $9.22 and $6.97, respectively, in lots of 10,000.

Speaking of volume controls, Maxim Integrated Products' MAX5440 controller is another chip that lets circuit designers do away with potentiometer control (Fig. 3). Its debounced rotary-encoder interface eliminates the need for an external microcontroller, GPIO, or debounce circuitry.

The rotary-encoder interface uses gray-scale coding to move the wiper up and down a 40-k½ resistor string. A mute function sets all wipers to maximum attenuation when activated and returns the wipers to their previous position when deactivated. A shutdown feature sets the wipers to maximum attenuation. Deactivating shutdown returns the wipers to their previous position.

On the chip's output, buffered wiper outputs connect directlyto the audio circuit's power amplifier. An integrated bias generator provides the necessary (VDD ? VSS)/2 voltage for unipolar input signals. An open-drain LED-mode indicator specifies whether the chip is in volume or balance control mode. Prices start at $1.47 for quantities of 1000 units and up.

For multimedia monitors and notebook computers, Maxim's MAX9777 and MAX9778 audio amplifiers combine a stereo 3-W bridge-tied load (BTL) audio amplifier, stereo headphone amp, headphone sensing, and a 2:1 input multiplexer. (This is something of an oversimplification, but the BTL amp is a descendant of the old Class AB, except with monolithic amplifiers replacing discretes.)

These amps offer 0.002% total harmonic distortion plus noise (THD+N). With their 100-dB PSRR, they can operate from noisy supplies without a regulator. Normal supply current is 13 mA, and there's a 10-µA shutdown mode. A headphone-sense input automatically detects the presence of a phone in the headphone jack. For control, the MAX9777 has an I2C interface, and the MAX9778 has a parallel bus. Prices start at $1.25 in lots of 1000 and up.

Here's a conundrum: Are the parts below analog or digital? For multiplexing digital and analog audio, Intersil offers its ISL54400, ISL54401, and ISL54402 dual 2:1 multiplexing audio/data switches (Fig. 4). They combine high bandwidth, low-capacitance switches for data signals with very low-distortion, low-capacitance switches for audio. As a result, they can be used alternately for USB full-speed data download, or for 20-mW per channel MP3 encoded stereo audio playback through the same jack.

The ISL54400 includes USB cable detection and data-rate negotiation hardware functions. The ISL54401 includes USB cable detection but not the data-rate negotiation hardware functions. The ISL54402 is a basic audio/data switch. The ISL54400 costs $1.07, the ISL54401 is $1.04, and the ISL54402 is $0.79, all in 1000-unit quantities.

Only a few digital-to-analog converters (DACs) have popped up lately. Instead, we're seeing DACs become integrated into DSPs and codecs. Bucking that trend, AKM Semiconductor introduced the AK4342 for digital radios, music players, and personal media players. The chip is a 24-bit stereo DAC with a ground-referenced, capacitor-less headphone amplifier and a 2-V rms line-output amplifier, as well as an ac-coupled auxiliary line-out.

To achieve a line output that connects directly to home audio amplifiers and receivers, the AK4342 uses an internal charge pump to generate a negative rail from a single +3.3-V power supply. The charge pump also is used for a 62.5-mW dccoupled headphone amplifier. Performance specs include 100-dB dynamic range and ?88-dB THD+N. Control is via I2C. Pricing starts at $1.80 in 10,000-unit lots.

On the other side of the data-converter equation, Wolfson Microelectronics' WM8781 is a high-input voltage 24-bit sigmadelta analog-to-digital converter (ADC) for DVD players, personal video recorders, set-top boxes, and studio audio processing equipment. Its extended clocking scheme enables it to interface to a wide range of host processors.

"High-input voltage" means the ADC accepts stereo linelevel inputs. "Extended clocking scheme" refers to the chips' "384fs" capability, which indicates that the processor clock runs at 384 times the audio sampling frequency. The WM8781s themselves sample at up to 192 kHz, allowing 128x, 64x, or 32x oversampling. Digital audio output word lengths from 16 to 24 bits and sampling rates from 8 to 192 kHz are supported. The WM8781 costs $1.59 in 10,000-unit quantities.

Beyond audio and video, there still has been a good deal of activity in new instrumentation amplifiers and data converters.

For example, Analog Devices has introduced a family of high-speed 10- and 12-bit ADCs for broadband communications and wireless infrastructure applications, such as cablemodem termination systems, third-and fourth-generation microcell and picocell basestations, and fixed point-to-point radios. These applications all are characterized by the need for low power consumption coupled with high conversion performance.

The family's flagship device, the 12-bit, 250-Msample/s AD9230, operates from a single 1.8-V supply and dissipates 425 mW. It integrates an on-chip reference and a track-andhold amplifier. On the output side, circuit designers may choose either of two parallel low-voltage differential signaling (LVDS) output modes (ANSI-644 and IEEE 1596.3 reduced range link).

A double-data-rate (DDR) mode halves the required number of parallel outputs. Combined with the IEEE 1596.3 reduced range link low-voltage differential signaling (LVDS) option, the DDR reduces power consumption to 385 mW. In terms of ac performance, signal-to-noise ratio (SNR) is 65.5 dBfs, and spurious-free dynamic range (SFDR) is 82 dBc with a 70-MHz input.

Other 12-bit family members are rated for 210 and 170 Msamples/s and there are 10-bit chips in the same speed grades. Sampling now, full production is scheduled for September. The fastest speed grade of the 12-bit AD9230 costs $59 per unit in 1000-piece quantities. The 10-bit, 250-Msample/s AD9211 is priced at $39.

For battery-powered data-acquisition systems, Linear Technology believes its 14-bit, 600-ksample/s LTC1408 multi-input ADC uses less than one-tenth the power and fits into a space one-fifth the size of anything with close to its performance. This three-wire serial ADC in a 32-pin (5- by 5-mm) QFN package operates from a single 3-V supply, with a typical power dissipation of 15 mW. When it isn't converting, power dissipation drops to 3.3 mW in Nap mode (its internal 2.5-V reference stays active) and to 6 µW in Sleep mode.

"Multi-input" means it has six simultaneously sampled differential inputs. But obviously, the price you pay for sampling multiple different inputs is that the 600-ksample/s conversion rate gets divided among them. Whatever input arrangement is selected, the six conversion results are delivered sequentially to a high-speed DSP serial port via a threewire interface. Power options are ±1.25 V bipolar or 0 to 2.5 V unipolar. Pricing begins at $8.95 in 1000-piece lots.

On the instrumentation amplifier side, Cirrus Logic has expanded its high-precision instrumentation family with the dual-channel CS3004 and CS3014 and single-channel CS3003 and CS3013. The CS3013 and CS3014 are lowerpower versions of the CS3003 and CS3004.

Though all of the amplifiers operate from single 2.7- to 5-V or dual 1.35- to 2.5-V supplies, the 3003/04 draw 1 mA per amp, and the 3013/14 draw 500 mA per amp. Equivalent input-noise voltage is 17 nV/√Hz in the 3003/04 and 25 nV/√Hz in the lower-power-consumption 3013/14. Open-loop gain is 150 dB in the 3003/04 and 135 dB in the 3013/14.

Input leakage current and offset voltage are 100 pA and 5 µV for the single-channel parts (100 pA and 10 µV for the duals) with offset voltage drift of 0.05 µV/°C in either case. The dual-amplifier CS3004 and CS3014 cost $1.52 in quantities of 1000.

For medical/instrumentation applications, STMicroelectronics offers a new, ultra-low-noise, wide-bandwidth op amp—the TSH300 (Fig. 5). That low-noise claim is quantified on the datasheet as a 0.65-nV/ÃHz (typical) equivalent input-noise voltage. That's coupled with a 200-MHz bandwidth at a gain of 5 (gain-bandwidth product is 1 GHz) and a 230-V/µs slew rate. SFDR is 55 dBc. It operates from 4.5 to 5.5 V on either single or dual supplies. The TSH300 costs $1.50 each for lots up to 5000.

National Semiconductor has added nine single, dual, and quad op amps built on its biCMOS VIP50 process technology to the six it announced last fall (Fig. 6). The LPV531, LMV654, LMV792, LMV796, and LMV797 low-power, low-voltage amplifiers are optimized for gain-bandwidth product performance. The LMP7704, LMP7712, LMP7715, and LMP7716 boast less than 220-µV input offset with guaranteed input bias of less than 50 pA and up to 12-V operation.

The LMV79x series features 5.8-nV/√Hz noise and 100-fA input bias currents. The LPV531 micropower op amp has adjustable gain-bandwidth control and a power-level adjust feature. The latter enables it to alternate between standby and full-power mode by varying the bias voltage on a single external resistor.

The 12-MHz, unity-gain bandwidth LMV654 quad amplifier requires significantly less power than equivalent competing chips, consuming 400 µA while maintaining a 12-MHz unity-gain bandwidth and a 17-nV/√Hz input-referred noise voltage. The LMV792's shutdown feature reduces power consumption to less than 1 µA in idle mode. The LMV796 and LMV797 fit applications in which system shutdown replaces localized shutdown requirements.

Among the other new VIP50-based chips, the LMP7712 dual amp offers low offset and noise as well as a 100-dB CMRR and PSRR.

The LMP7704 rail-to-rail quad precision amplifier eliminates the large offset glitch associated with conventional CMOS rail-to-rail input amplifiers. A patented correction technique reduces the large offset-voltage temperature coefficient commonly found in CMOS precision amplifiers. All nine op amps range from $0.75 to $2.49 in 1000-unit lots.

Operating down to 1.8 V, ADI's AD8500 rail-to-rail precision op amp looks to battery-powered applications like electrocardiograms, pulse monitors, glucose meters, smoke and fire detectors, security systems, gas detectors, backup battery sensors, insulin pumps, and ultraviolet detectors in cellular handsets.

It specifies a 1-µA maximum supply current while operating from a single +1.8- to +5.5-V supply or a ±0.9- to ±2.75-V dual supply. The low voltage makes it possible to use ordinary batteries over their full discharge profile. The chip guarantees a 1-mV max offset and 1-pA input bias, and it costs $0.70 each in 1000-piece lots.

Beyond amplifiers and converters, Maxim has introduced a truly analog quarter-size alternative for the ceramic resonators and crystals normally used in low-speed USB applications. The MAX7393/7394 fixed-frequency, non-phase-locked-loop precision silicon oscillators boast ±0.25% accuracy from 0°C to 85°C (±0.5% accuracy from ?45°C to 85°C).

Available for frequencies from 922 kHz to 48 MHz, they can be connected to any microcontroller without the need for impedance or capacitive matching. The MAX7393's auto-sense capability senses a microcontroller's oscillator circuit and enables itself when the microcontroller's oscillator turns on. The MAX7394 uses a simple enable pin. In shutdown mode, maximum current is 2 µA. Prices start at $0.40 in lots of 10,000 and up.

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