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The Non-Inverting Amplifier Output Resistance
Wednesday, December 23rd, 2009Summary:
It is customary to consider the output resistance of the non-inverting amplifier as being zero, but why is that? An Op Amp’s own output resistance is in the range of tens of ohms. Still, when we connect the Op Amp in a feedback configuration, the output resistance decreases dramatically. Why?
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Design a Differential Amplifier the Easy Way with Mathcad
Thursday, November 19th, 2009Summary:
For those of you who have Mathcad, designing a differential amplifier is really easy.
Let’s say you need to design a unipolar to bipolar converter and you decide to use a differential amplifier for this task. You know the input and output voltage range and you need to calculate the resistors based on a voltage reference you have in the system. All you have to do is to create a Mathcad file for a quick response. Then store it some place for future designs.
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Design a Unipolar to Bipolar Converter for a Unipolar Voltage Output DAC
Monday, November 2nd, 2009Summary:
Unipolar to bipolar converters are useful when we have to have a unipolar component to do a certain job in a mixed signal design environment. For example, Digital to Analog Converters (DACs) may have the output voltage range 0 to 2.5 V, or 0 to 5 V, while the design asks for a range of –5 V to +5 V. To comply with this requirement, we have to design a unipolar to bipolar converter which will be inserted between the DAC output and the following bipolar stage.
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Design a Bipolar to Unipolar Converter to Drive an ADC
Monday, October 26th, 2009Summary:
Most ADCs have a unipolar input range that can be a problem when designing bipolar circuits. Some common ADC input voltage ranges are 0 to 2.5 V, or 0 to 5 V. However, the analog circuit that drives the ADC can have voltage swings of, –1 V to +1 V, –2 V to +2 V , –5 V to +5 V, and so on. Bringing the ADC input below ground is a big No-No, because the current from input will flow through the chip substrate creating irreversible changes in the ADC and damage it. So, how do we connect a bipolar front end circuit with a unipolar ADC? Enters the bipolar to unipolar converter. Let’s design one.
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How to Derive the Instrumentation Amplifier Transfer Function
Sunday, August 30th, 2009Summary:
The Instrumentation Amplifier (IA) resembles the differential amplifier, with the main difference that the inputs are buffered by two Op Amps. Besides that, it is designed for low DC offset, low offset drift with temperature, low input bias currents and high common-mode rejection ratio. These qualities make the IA very useful in analog circuit design, in precision applications and in sensor signal processing.
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Summary:
What is this circuit good for? It creates a single-ended-input-differential-output amplifier, in which VCM is the common mode and the main signal, in this case the average (VA+VB)/2 rides on top of VCM. It is very useful for fully differential circuits in low noise applications, because differential amplifiers help reduce the common mode noise. VCM in this case, sets the common mode to a useful level as required by the design.
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How to Derive the Non-Inverting Amplifier Transfer Function
Saturday, August 29th, 2009Summary:
One of the most common amplifiers in Analog Design is the non-inverting amplifier. How do you derive its transfer function?
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