66.5.3. Concerns with Higher Supply Voltage

One is power dissipation it will increase for the same coefficient current. If this voltage is higher necessarily the power dissipation it will be a problem and also instantaneously if the output voltage here it is higher, then that may exceed the breakdown limit of the device, so this may not be allowed.

As you increase the supply voltage, two main concerns arise. First, power dissipation will increase. Power dissipation is calculated based on the product of voltage and current. Therefore, maintaining the same current level while increasing voltage will raise the power being dissipated as heat. This can lead to overheating, which may damage components. Second, if the output voltage surpasses the breakdown limit of the transistor used in the circuit, this could cause the transistor to fail. Thus, designers must ensure that any increase in voltage does not push the device's limits.

Imagine you're driving a car. If you decide to push the accelerator down harder (analogous to increasing supply voltage), the car will go faster (higher current). However, if you push too hard and exceed the car’s safety limits (like the breakdown voltage of a device), you risk damaging the engine (the transistor). Furthermore, driving at high speeds generates more heat (power dissipation), which can damage engine components if not properly cooled.

So, the natural question or a natural intuition it may be or rather I should say smarter intuition maybe, that can I increase this rather decrease this slope without changing this voltage? Well, that is also possible maybe we can keep this point here and then we can try to decrease this and decrease this slope of the second mirror.

The quest for increasing voltage gain without raising the supply voltage leads to the need to analyze the circuit’s slopes. Ideally, decreasing the slope of the output load (the second mirror) can yield a higher gain based on the relationship of gain to slope. Therefore, while maintaining the same operating point, an alternative approach is employed where we use more sophisticated designs, allowing for a higher output without needing to increase voltage supply, thereby avoiding the breakdown concerns discussed earlier.

Think of pouring juice into a glass. If the juice flows too quickly (high slope), it may overflow. To avoid this, you can pour more gently or tilt the glass (decreasing the slope). This adjustment allows you to control the amount without needing a bigger glass (changing the supply voltage). Thus, it's possible to manage the flow without increasing the height of the glass.

So, we can probably you can terminate this characteristic here. Which means that, in case if we have an option to have I-V characteristic which is not completely linear, but over this range it is linear and then it is having sharp non-linear to terminate to the and to the available supply voltage.

To achieve better voltage gain while avoiding concerns with increased supply voltage, the use of active loads becomes relevant. Active loads allow for an I-V characteristic that isn't completely linear but provides good linearity within certain ranges and reaches a sharp non-linearity that caps at the supply voltage. This means the device can efficiently utilize the available voltage range without risking breakdown or excessive power dissipation while maximizing gain.

Imagine a race car that has a speed limiter (akin to an active load). It can accelerate smoothly up to the speed limit without exceeding it. Once it reaches that limit, the engine doesn’t overwork or break down, allowing a consistent performance without risking damage. In this scenario, the speed limit is like the available supply voltage, and the smoother acceleration represents maintaining good gain.

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