As the use of portable devices such as phones, tablets, and laptops increases, the demand for audio quality is also increasing. Audio quality has the task of implementing high performance while minimizing power consumption. This is where engineers' concerns begin.

In particular, for portable devices featuring light and small sizes, integrated solution size and low power consumption are required. Accordingly, Hwang Jeong-gi, Manager of Maxim Korea, presents five tips for selecting a good audio codec.

Vice President Hwang said that in line with recent trends in portable devices, the input section, DSP core, and output section of the audio codec must have distinctive features along with size and low power consumption.

1. Let's look at the input terminal; supports digital and analog signal interfaces.
Maxim's MAX98091 stereo audio codec supports three input terminals, all of which can handle stereo single-ended/differential analog signals, and two of them can also handle digital microphone signals. For example, users can use all three terminals as stereo analog inputs, or use two terminals as digital microphone interfaces and the rest as general audio analog interfaces. This means that Maxim's audio codec supports various interfaces, including analog and digital.

The stereo ADC processes external signals, where the input signals from two digital microphones are processed for use in noise cancellation and echo cancellation functions. It is also designed to support a variety of applications in portable devices, such as converting general analog input signals such as radio directly to digital.

“Maxim supports an additional feature called jack detection, which is intended to distinguish polarity and other characteristics depending on the type of headset,” said Vice President Hwang.

2. How far have you reached the performance limits of the codec DSP?
It is also important to look at the performance of the DSP core, which has emerged as the core of the audio codec. Maxim calls the core, which plays a role in adding sound effects to the signals coming from the input stage and ADC, FlexSound® DSP. The FlexSound DSP core has optimized biquad filters, equalizers, dynamic range, digital gain, and digital filtering.

Mr. Hwang Jeong-gi, the head of the company, said, “It provides various voice filter setting functions through the biquad filter function on the voice path where the signal comes in from the microphone and is transmitted to the AP. Also, on the playback path where the signal is transmitted from the AP to the amplifier or headset, the signal is tuned through the 7-band parameter equalizer. Through this process, various effects can be applied to music sounds such as jazz and pop.” While the existing equalizer methods were 1, 2, and 5 bands, Maxim’s MAX98091 codec supports up to a 7-band equalizer.

It is worth noting that the dynamic range control has been supplemented with compression and expander functions. These change the high and low ranges depending on the user environment. And the DIA filtering provided on the voice path and playback path respectively provides an IIR filter for human voice and an FIR filter for music.

3. Do I need to install a separate amplifier on the codec output?
If the output stage does not have its own speaker amplifier, a separate amplifier must be used. The same goes for receivers and headphone amplifiers. Maxim's stereo audio codec (MAX98091) has a built-in amplifier that can be used as a line out or receiver. Since it is a stereo amplifier, it has a stereo speaker amplifier output. In addition, the headphone amplifier has the effect of reducing current consumption by driving Class H. Using a Class H amplifier reduces power consumption, which is a reason for portable devices, and reduces peripheral components by internally building a charge pump.

4. Is it a low power codec or not?
One of the most important factors to consider in portable devices is power consumption. In order to make the limited battery last longer, power consumption at each device level must be minimized. The key point of Maxim's stereo audio codec is that it uses only 4mW based on stereo speaker playback. Mr. Hwang said, "The important thing is that low power support is a key technology of the amplifier not only for headphone playback conditions but also for stereo speaker playback conditions that consume a lot of power." In other words, the standby operation of the audio codec, DSP, ADC, and other power-consuming technologies must be configured with low power to satisfy the low power issue that is a concern in portable devices.

5. Does it meet the chip size requirements for device design?
Lastly, chip size. In the circuit design of portable devices, if the solution size is large, it can be a hindrance no matter how high the performance is. How much the size of the chip itself is reduced is directly related to how many peripheral components are integrated. In the case of the MAX98091 audio codec, it is supported in a very small package of 3.2 x 3.6 mm. By making it smaller, we were able to integrate things like amplifiers and output capacitance, giving us more room for circuit design.

In addition, it is also essential to check the interface to see if it supports all of the most commonly used digital interfaces. For example, you should check if it supports the I2S Interface, which is the most commonly used audio format, and if it supports the LJ/RJ/TDM digital audio interface, added Mr. Hwang.