Headphone driver

A magnetodynamic headphone with a typical impedance of 32 Ω at 1 kHz produces a sound pressure level of 98 dBSPL at 1 mW electrical input power. Over the audio frequency range (20 Hz−20 kHz) the impedance may vary between 30 Ω and 100 Ω. For a flat frequency characteristric the headphone should be driven by a voltage.

A high-performance single-ended voltage output DAC delivers a voltage of 0.2Vpp with a midscale value of 0.9 VDC. Its small-signal output impedance is less than 100 Ω. It may maximally sink and source a current of 100 µA. Its output voltage noise spectral density at midscale output is below 4nV/ Hz.

A high-performance audio amplifier should drive this headphone such as to produce a sound pressure level of 110 dBSPL at full-scale DAC output with a signal to noise ratio of at least 96dB.

The total harmonic distortion for sinusoidal input signals from 20Hz to 5kHz and from 60dBSPL to 110dBSPL output level should be below 0.03%. For frequencies above 5kHz, this figure should be met for power levels from 60 dBSPL to 90 dBSPL.

The audio amplifier must operate from 0 to 70 degrees Celsius.

The circuit must operate at a power supply of 1.8 V ± 5%.

The quiescent power dissipation should be below 2mW.

The circuit must be realized in a CMOS18 process.