& amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp lt img src=' ' alt='Figure 1'& amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp amp gt įigure 1. The differential gain of the circuit is equal to Just like in a regular op amp, the high open-loop gain combined with the feedback effectively forces the two inputs to bias at nearly identical voltages, often called “virtual ground.” Circuit analysis is based on the concept of virtual ground.
Figure 1 shows four external resistors feeding a portion of the differential output back into the differential input. A regular op amp features high open-loop gain between the differential input and the one output a fully differential op amp features high open-loop gain between the differential input and the differential output.įeedback should also be applied differentially. Just like a regular op amp, it has two inputs, but unlike a regular op amp, it also has two outputs, labeled –OUT and +OUT. Let’s take a closer look at how a differential op amp works. Therefore, to use those components, you have no choice but to convert your analog signal to fully differential at some point in your signal chain. This fully differential input requirement is near universal for ADCs that convert at a high sample rate (e.g., pipeline ADCs at >10Msps) as well as for ADCs that achieve very high resolution, high linearity and low noise (e.g., SAR ADCs at ≥18 Bit and ≥100dB SNR). For a given noise floor, doubling the maximum signal swing results in a 6dB improvement in the signal-to-noise ratio (SNR).įinally, some semiconductor components mandate, per the data sheet, that you provide a fully differential signal into the input. That is because either of the two nets can be higher or lower than the other, which effectively doubles the signal swing. But a fully differential signal can vary from –5V to 5V, for 10V P–P. For example, in a system that is powered from a single 5V supply, a traditional single-ended signal can vary at most 5V. For example, if power supply noise couples equally to both conductors that carry your fully differential signal, then the difference signal may remain undisturbed.Īnother benefit of fully differential signal processing is that you can squeeze more signal into a given supply voltage range. One benefit of fully differential signal processing is that it can reduce sensitivity to external interference, such as power supply noise, ground bounce or electromagnetic interference (EMI). The analog signal is defined as the voltage difference between these two nets. Whenever one voltage goes higher, the other voltage goes lower by the same amount.
Fully differential means that two nets each vary with signal. But there are times when it is better, or necessary, to make the analog signal fully differential. LTC6362 key specifications Supply CurrentĪn analog signal is usually represented as one signal measured with respect to a fixed potential such as ground, also known as a single-ended signal. The LTC6362 is unique in that it features differential outputs, low power consumption and accurate DC offset voltage (see Table 1). Many alternative op amps of this fully differential nature are optimized for very high speed operation,resulting in high power consumption and lack DC accuracy. The LTC6362 op amp produces differential outputs, making it ideal for processing fully differential analog signals or taking a single-ended signal and converting it to fully differential. Precision Fully Differential Op Amp Drives High Resolution ADCs at Low Power
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