Mobile devices with increasing performance demands, limited
High performance while maintaining battery life requires trade-offs
Low-power operational amplifiers contribute to 'power-performance' optimization


High performance and low power are conflicting characteristics, but they are becoming increasingly important values in many applications, especially battery-operated mobile devices.

These applications range from mobile biometric monitoring to monitoring machinery and systems in industrial settings. The need for improved performance and maximum battery life is also present in consumer products such as smartphones and wearables.

Since the batteries available in mobile devices have limited energy, efficient components that minimize current consumption during operation are required to maximize usage time. In addition, power consumption can be reduced to maintain the same battery usage time even with lower capacity batteries, thereby reducing the size, weight, and cost of the device.

Temperature management is also an important consideration. This issue can also be positively affected by the use of efficient components. Cooling devices take up space, and by using more efficient components, heat generation can be reduced and the size of the cooling device can be reduced.

There are a variety of low-power and ultra-low-power (ULP) components available on the market. Thomas Brand, FAE for Analog Devices Central Europe, explores low-power operational amplifiers in his article, “Power Performance Trade-Offs in Operational Amplifiers.”

◇ Trade-off between power consumption and performance

Selecting the right operational amplifier requires considering tradeoffs related to operational amplifier power dissipation. Typically, lower power dissipation translates to lower bandwidth. However, this can vary depending on the specific amplifier architecture and stability requirements.

Generally, the higher the parasitic capacitance and inductance, the lower the bandwidth. For example, transimpedance amplifiers (current feedback amplifiers) have relatively high bandwidth but poor precision. However, there are several methods to increase the bandwidth-to-power ratio.


The gain bandwidth (GBW) can be calculated as follows. In this formula, G _m is the transconductance (ratio of output current to input voltage (I _OUT /V _IN )), and C is the internal compensation capacitance.

The classical way to increase the bandwidth is to increase the bias current. However, this increases the power consumption instead of increasing Gm. Ideally, the load capacitance should not affect the bandwidth at all, since the compensation capacitance usually determines the dominant pole. Although limited by the physical characteristics of the amplifier, lower capacitance generally provides higher bandwidth. Low capacitance may impair stability, but low noise gain usually improves stability.

However, it is difficult to drive large capacitive loads at lower noise gain in practice. Another tradeoff when using low-power operational amplifiers is high-voltage noise. Typically, input-referenced voltage noise is the largest contributor to the amplifier's total output wideband noise, but resistor noise can also be significant. The input-side noise sources are a significant contributor to the total noise. Examples include collector shot noise and drain thermal noise.

1/f noise (flicker noise) depends on the architecture and is caused by special defects in the component materials. Therefore, it can account for a significant proportion depending on the component size. Current noise decreases as the power level decreases, but in the case of bipolar amplifiers, this noise can also be significant. In the 1/f section, 1/f current noise can account for a significant proportion of the total 1/f noise of the amplifier output.

Another trade-off is distortion performance and drift values. Lower power operational amplifiers exhibit higher total harmonic distortion (THD), but in bipolar amplifiers, as with current noise, lower power supply current reduces input bias and offset current.

Another characteristic of the operational amplifier is the offset voltage. The offset voltage is affected by the use of input-side components, and does not significantly degrade performance at low power. Therefore, VOS and VOS drift are constant for the power value. The external circuit and feedback resistor (R _F ) also affect the performance of the operational amplifier. A large resistor value reduces dynamic power and harmonic distortion, but increases output noise and increases bias current-related effects.

To further reduce power consumption, many devices offer standby or sleep modes. These modes allow the device features to be disabled when not in use and re-enabled when needed, although lower power amplifiers typically have longer startup times. The tradeoffs listed so far can be summarized as follows:

Brand FAE proposes the ' ADA4945-1 ' bipolar differential amplifier as a product that combines these characteristics. It has low DC offset and DC offset drift, and excellent dynamic characteristics, making it suitable for use as an ADC driver in high-resolution data acquisition and signal processing applications. Below is the AD4022 ADC driving using the ADA4945-1.

The ADA4945-1's multiple power modes allow you to optimize performance and power to meet your needs. For example, the full power mode is well suited to the ' AD4020 ', while the low power mode is well suited to the lower sample rates of the ' AD4021 ' or 'AD4022'.