Home Theater in a Box (HTiB)

Audio Subsystem: Home Theater in a Box (HTiB) Solutions from Texas Instruments

Description

Audio Subsystem: Home Theater in a Box (HTiB)

**PCM9211 can act as both an ADC and an audio transceiver

The core subsystems include:

Digital-Input Class-D Speaker Amplifier

Output Power per Channel

  • After determining the number of speakers in a system, specify the output power for each channel.
  • Maximum power is decided primarily by power supply (output voltage and current) and speaker impedance.
  • Efficiency of Class-D amplifiers is typically between 80% and 90%, which reduces demands on power-supply designs when compared to Class-AB amplifier requirements.
  • The maximum input signal level dictates the required power amplifier gain to achieve the desired output power.
  • For best noise performance, the gain should be as low as possible.

Output Filter Design

  • Most of TI’s Class-D amplifiers operate without a filter when speaker wires are less than 10 cm.
  • EMI from high-frequency switching is a major design challenge.
  • When speaker wires are long, place a second-order low-pass (LC) filter as close as possible to the amplifier’s output pins.
  • The filter must be designed specifically for the speaker impedance because the load resistance affects the filter’s quality factor, or Q.
  • A ferrite bead may also eliminate very high-frequency interference.

Medium- and High-Power, Analog-Input Class-D Speaker Amplifiers

Output Power per Channel

  • Maximum power is decided primarily by power supply (output voltage and current) and speaker impedance.
  • Efficiency of Class-D amplifiers is typically between 80% and 90%, which reduces demands on the power supply design.
  • The maximum input signal level dictates the required power amplifier gain to achieve the desired output power.
  • For best noise performance, the gain should be as low as possible.

Output Filter Design

  • Most of TI’s Class-D amplifiers operate without a filter when speaker wires are less than 10 cm.
  • When speaker wires are long, place a second-order low-pass (LC) filter as close as possible to the amplifier’s output pins.
  • The filter must be designed specifically for the speaker impedance because the load resistance affects the filter’s quality factor, or Q.
  • A ferrite bead may also eliminate very high-frequency interference.

Audio Converters

Reducing Noise on Microphone Inputs

  • Microphone signals are susceptible to noise injection because of the low peak-to-peak range of 10 mV.
  • Placing the codec or ADC close to the microphone often conflicts with user preference, industrial design or mechanical design requirements.
  • Look for devices that can work with digital microphones or have differential inputs, both of which provide significantly better noise immunity.

Processing Allocation and Software Re-usability

  • Host processors in handheld consumer electronics are being given more tasks, pushing processor MIPS allocations and design schedules.
  • One solution is to offload a number of audio functions to a DAC or codec.
  • Audio functions include 3-D effects, equalization, notch filters or noise cancellation.
  • Look for devices with broad, easy software re-usability and the ability to allocate the processing to either input or output functions.

Application notes & user guides

Application Notes (4)

Title Abstract Type Size (KB) Date Views
HTM 8 KB 24 May 2004 21721
HTM 8 KB 02 Oct 2000 3098
HTM 9 KB 24 Aug 1999 737
HTM 8 KB 23 Aug 1999 226

User Guides (3)

Title Abstract Type Size (KB) Date Views
htm 8 KB 28 Apr 2009 174
pdf 676 KB 06 Aug 2006 511
pdf 757 KB 16 Jun 2006 482

Selection & solution guides

Solution Guides (1)

Title Abstract Type Size (KB) Date Views
PDF 5.43 MB 15 Dec 2011 2083

Support & community

Other Support