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This 10-page Application Note describes techniques to use for post-production testing and debugging of video platforms using advanced video (ADV) series devices. Advanced video systems are becoming more complex and the video chains contain more and more links. Employing built-in self-tests on video evaluation systems allows a significant increase in productivity by automated tests. The ADV parts include features that allow finding a short, an open, or a problem in video processing, audio processing, or data/control circuitry. Many of ADV parts contain internal pattern generators, synchronization detection circuitry (for video), and built-in external memory tests that can be used to test a platform and facilitate the process of debugging a potentially faulty platform. To test the system, the final video processing circuitry must contain a microprocessor that includes a connection to tested video parts and a postproduction program that can be enabled and run at least once after production.
An HDMI mux is commonly used to increase the number of HDMI inputs in a system, but this results in two cascaded stages that handle the TMDS signals before they are digitally processed in the receiver. Each stage contributes jitter that degrades the quality of the signal. This can present a challenge for HDMI compliance tests, especially when operating at higher data rates. This 2-page Application Note shows how a synchronous mux can perform better because it removes most types of jitter and presents a clean signal to the HDMI receiver.
A microphone preamp circuit amplifies a microphone’s output signal to match the input level of the following device. Matching the peaks of the microphone’s signal level to the full-scale input voltage of an ADC makes maximum use of the ADC’s dynamic range and reduces the noise that subsequent processing may add to the signal. The MEMS microphone has a single-ended output, so a single op amp stage can be used as a preamp to add gain to the microphone signal or to buffer the output. This Application Note covers some of the key op amp specifications to consider for a preamp design, shows a few basic circuits, and provides a table of Analog Devices op amps that are appropriate for a preamp design. The ADMP504 MEMS analog microphone with 65 dB SNR is used as an example to describe different design choices.
This circuit provides a complete solution for converting HDMI/DVI to VGA (HDMI2VGA) with an analog audio output. Using the low-power ADV7611 HDMI receiver, it is capable of receiving video streams up to 165 MHz. Powered from a USB cable, it works for resolutions up to 1600 × 1200 at 60 Hz. The circuit uses EDID content to ensure that the video stream from the HDMI/ DVI source is at the highest possible resolution supported by the HDMI source, converter, and VGA display.
This circuit interfaces an analog MEMS microphone to a microphone preamp. The ADMP504 consists of a MEMS microphone element and an output amplifier. Analog Devices’ MEMS microphones have a high signal-to-noise ratio (SNR) and a flat wideband frequency response, making them an excellent choice for high-performance, low-power applications. The SSM2167 low-voltage, low-noise mono microphone preamp is a good choice for use in low-power audio signal chains. This preamp includes built-in compression and noise gating, which gives it an advantage for this function over using just an op amp in the preamp circuit. Compressing the dynamic range of the microphone signal can reduce the peak signal levels and add additional gain to low level signals. Noise gating attenuates the level of signals below a certain threshold, so that only desired signals, such as speech, are amplified, and noise in the output signal is reduced. These features help to improve the intelligibility of the voice signal picked up by the microphone.
Keypad Decoder and I/O Port Expander
The ADP5586 I/O port expander and keypad matrix decoder is designed for portable and non-portable devices that require a large keypad matrix and/or expanded I/O lines. Its 10 configurable input/outputs enable functions such as 5 × 5 keypad decoding. Handling all key scanning and decoding, it frees the main processor from having to monitor the keypad, thereby reducing power consumption and increasing bandwidth for other functions. It flags the main processor via an interrupt line when new key events or general-purpose input changes have occurred. An on-chip FIFO stores up to 16 events that can be read via an I2C-compatible interface. It also includes programmable logic capabilities and a reset generator, allowing the integration of other common functions onto board designs. Operating on a single 1.65-V to 3.6-V supply, the ADP5586 draws 30 μA with one key pressed and 1 µA in standby mode. Available in 6-ball WLCSP package, it is specified from –40°C to +85°C and priced at $0.75 in 1000s.
High-Side Power Switch with logic-level control
The ADP196 high-side power switch disconnects unused loads from a power supply to extend battery life in mobile phones, digital cameras, and audio devices. It also works well to prevent in-rush current in optical modules. With 27‑mΩ on-resistance, the N-channel MOSFET switching element minimizes power loss while handling continuous currents of up to 3 A. An on-chip level shifter ensures logic compatibility with modern processors and controllers. Operating on a single 1.8-V to 5.5-V supply, the ADP196 draws 25 μA of ground current when enabled and 250 nA when shutdown. Available in 6-ball, 1-mm × 1.5-mm WLCSP or 6-lead 2-mm × 2-mm LFCSP packages, it is specified from –40°C to +85°C and priced at $0.50 in 1000s.
Stereo PDM-to-I2S or PDM-to-TDM Converter
The ADAU7002 converts a stereo PDM bit stream into a 20-bit PCM output. The PDM data can be provided by a digital microphone, such as the ADMP521, or other PDM source. The audio data is down sampled by 64× and output in either I2S or TDM format at a sample rate between 4 kHz and 96 kHz. The device automatically shuts down when the clock is removed. Operating on a single 1.62-V to 3.6-V supply, the ADAU7002 draws 1.33 mA at 3.6 V, 0.67 mA at 1.8 V, and 1 µA in shutdown mode. Available in an 8-ball WLCSP package, it is specified from –40°C to +85°C and priced at $1.04 in 1000s.
High-efficiency eight-string white LED Driver for LCD backlight applications
The ADD5201 white-LED driver for backlight applications uses a high-efficiency, current-mode step-up converter to provide eight regulated constant-current sources—each capable of driving up to 30 mA—to illuminate eight strings of series-connected LEDs. The ±1.5% current matching ensures uniform LED brightness. A PWM input supports 8-bit resolution to control LED dimming in the 3% to 100% range. Four modes of PWM dimming are available for controlling the phase delay between individual current sources: fixed delay, phase shift, no delay, and direct. Multiple safety protection features prevent damage during faults, including overvoltage, undervoltage, open circuit, short circuit, and overtemperature conditions; and soft start prevents inrush current at startup. Operating with a 6-V to 21-V supply, the ADD5201 draws 2.5 mA in normal mode and 40 µA in shutdown mode. Specified from –25°C to +85°C, it is available in a 28-lead LFCSP package and priced at $1.67 in 1000s.
Jeff Ugalde, Ian Beavers, and Lie Dou, Deliver Quad-HD Video Over HDMI Cables, Electronic Design, 2013-03-05
Witold Kaczurba and Brett Li, HDMI Made Easy: HDMI-to-VGA and VGA-to-HDMI Converters, Analog Dialogue, 2013-02-04
Jerad Lewis and Paul Schreier, Low self noise: The first step to high-performance MEMS microphone applications, EE Times, 2012-11-28
Brett Li and Li Dou, HDMI I/O Solution and Reference Design, Global Electronics China, 2012-09-19
Jerad Lewis, Understanding Microphone Sensitivity, Analog Dialogue, 2012-05-01
Javier Calpe, Italo Medina, Alberto Carbajo, and María José Martínez, AD7879 Controller Enables Gesture Recognition on Resistive Touch Screens, Frontier Journal, 2012-05-01
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