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Components Selection

Resistor matching is very important in full differential amplifiers. The balance of the output on the reference

voltage depends on matched ratios of the resistors. CMRR, PSRR, and cancellation of the even-order

harmonic distortion diminish if resistor mismatch occurs. Therefore, it is recommended to use 1% tolerance

resistors or better to keep the performance optimized. Matching is more important than overall tolerance.

Resistor arrays with 1% matching can be used with a tolerance greater than 1%.

Place the input resistors very close to the HM2010 to limit noise injection on the high-impedance nodes. For

to operate at its best, and keeps a high voltage at the input making the inputs less susceptible to noise. In

Decoupling capacitor helps to stabilize voltage of power supply and thus reduce the total harmonic

distortion (THD). It can also be applied to prevent oscillation over long leads. A Low

Equivalent-series-resistance (ESR) capacitor of 1µF is required for decoupling and should be placed close

to the HM2010 to reduce the resistance and inductance on the trace between the amplifier and the capacitor.

For filtering lower-frequency noise signals, a 10µF capacitor could be placed near the audio power

amplifier.

The input capacitor and input resistor determine the corner frequency of the high pass filter. The corner

frequency (fc) is calculated with the Equation (2) below.

The corner frequency directly influences the low frequency signals and consequently determines output

bass quality.

PCB Layout

As output power increases, interconnect resistance (PCB traces and wires) among the audio amplifier,

load and power supply create a voltage drop. The voltage loss on the traces between the HM2010 and the

load results is lower output power and decreased efficiency. Higher trace resistance between the supply

and the HM2010 has the same effect as a poorly regulated supply, increase ripple on the supply line also

reducing the peak output power. The effects of residual trace resistance increases as output current

increases due to higher output power, decreased load impedance or both. To maintain the highest output

voltage swing and corresponding peak output power, the PCB traces that connect the output pins to the

load and the supply pins to the power supply should be as wide as possible to minimize trace resistance.

The use of power and ground planes will give the best THD+N performance. While reducing trace

resistance, the use of power planes also creates parasite capacitors that help to filter the power supply line.

(1)

(2)