The MAX9814 is a low-cost, high-quality microphone amplifier with automatic gain control (AGC) and low- noise microphone bias. The device features a low-noise preamplifier, variable gain amplifier (VGA), output amplifier, microphone-bias-voltage generator and AGC control circuitry. The low-noise preamplifier has a fixed 12dB gain, while the VGA gain automatically adjusts from 20dB to 0dB, depending on the output voltage and the AGC threshold. The output amplifier offers selectable gains of 8dB, 18dB, and 28dB. With no compression, the cascade of the amplifiers results in an overall gain of 40dB, 50dB, or 60dB. A trilevel digital input programs the output amplifier gain. An external resistive divider controls the AGC threshold and a single capacitor programs the attack/release times. A trilevel digital input programs the ratio of attack-to-release time. The hold time of the AGC is fixed at 30ms. The low-noise microphone-bias- voltage generator can bias most electret microphones. The MAX9814 is available in the space-saving 12-bump UCSP™ (1.5mm x 2mm) and 14-pin TDFN packages. This device is specified over the -40°C to +85°C extended temperature range.
The MAX9814 is a low‑cost, high‑quality microphone amplifier featuring automatic gain control (AGC) and an internal low‑noise microphone bias. It combines a fixed‑gain preamplifier, a variable‑gain amplifier (VGA) controlled by AGC, and a selectable output amplifier gain.
The datasheet provides electrical characteristics, absolute maximum ratings, pin descriptions, typical operating curves, and application notes such as programming attack/release times and package dimensions. It also includes ordering information and revision history.
| Supply Voltage Range | 2.7 V to 5.5 V |
|---|---|
| Gain Settings | 40 dB, 50 dB, 60 dB |
| Input‑Referred Noise Density | 30 nV/√Hz |
| Total Harmonic Distortion (THD) | 0.04 % (typ) |
| Microphone Bias Voltage | 2 V |
| Operating Temperature Range | -40 °C to +85 °C |
The device operates from 2.7 V to 5.5 V.
They are set by the external timing capacitor CcT and the tri‑level A/R input that selects the attack‑to‑release ratio.
The internal bias voltage is regulated at 2 V to drive most electret microphones.