audio/videoZONE Products for the week of August 4, 2003
AKM Says . . .
AK5356: Audio ADC Integrates Microphone Preamplifier
and Volume Control
Asahi Kasei Microsystems Co., Ltd. (AKM), a leading supplier of audio ICs for professional and consumer markets introduced the the AK5356, an enhanced 20-bit 2-channel A/D converter with built-in high-performance microphone preamplifier and analog volume circuit. The low-power device is designed for portable audio applications such as digital still cameras, cell phones and personal recorders.
The AK5356 is based on the previously released AK5354 20-bit ADC with
integrated recording volume control. It offers the same high performance
as the AK5354 while integrating an ultra-low-noise preamplifier (+40 ~ 60dB)
and a condenser microphone power supply. This combination of features delivers
low power, high gain and ideal overall performance characteristics for high-quality
recordings. In addition, the 1.8V digital power supply of the AK5356 enables
it to interface with today's low-power microprocessors and system-on-a chip
devices.
analogZONE Says...
The AK5354 was already a nice little part: A 20-bit ADC with a pair of line inputs on each side with switching and gain control. The gain control, in each ADC drive channel , allows for step variations from +28 dB to -52 dB, with the positive gain to -8 dB range being in 0.5 dB steps, and then increasing -- in a logarithmic-like function with further attenuation. To this part AKM has now added two microphone preamplifiers -- which also have stepped gain -- and a condenser microphone power supply. The outputs of the preamplifiers are taken to IC pins so that they could be used for other purposes, or filtered, or switched with other sources before coming back on chip.
The microphone power supply provides a nominal 2.16 V (at 1 mA max) from a 2.7-V input pin while the preamplifiers have feedback gain control in steps of +13 dB, +18 dB, +28 dB, and +33 dB. Gain error is within a ±1.5 dB window and the worst case SINAD is 60 dB at maximum gain and outputting -29.2 dBV. Isolation between channels is a typical 90 dB at maximum gain, with a maximum gain mismatch of 0.5 dB at all gain selections. PSRR worst case is a typical 46 dB at maximum gain.
The ADC offers a SINAD of 84 dB with th input PGA gain at 0dB and a -0.5 dBFS input; A-weighted SNR is 89 dB under these conditions with 100 dB isolation between channels. Post-conversion low-pass filtering gives a 0.1 dB passband of 17.4 kHz with a maximum ripple of ±0.1 dB. Post-conversion high-pass filtering sets the -3 dB point at 3.4 Hz (fs = 44.1 kHz) and the -0.1 dB point at 22 Hz, to give a total audio passband of 22 Hz to 17.4 kHz.
The separate power pins of the analog and digital parts of the circuit are specified for 2.5 V with a typical total consumption of 6 mA, although the digital rail can be operated down to 1.8 V to suit the following processor. The 2.7-V microphone power input consumes a typical 3.4 mA. Power-down reduces the total demand from the three supplies to a typical 10 µA.
The addition of the pre-amplifiers and the microphone power supply open up a number of new portable device sockets for the AK5356 where codec functions are not required.
The AL5356 is in production in a QFN-28 and is priced at $5.40 in 1000-piece lots. Evaluation boards are available.