Digital data line driver
AssigneeLevel One Communications, Inc.
InventorCheng C. Shih
Life of this patent
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Abstract
A cost-effective, low power and low distortion digital data line driver is disclosed with the capability to operate from a limited voltage source while maintaining wide output voltage swings. The line driver has the noise immunity attribute of a fully differential input device without all the usual complex CMFB circuitry normally required. The line driver provides a low distortion output with a low output impedance and maintains its impedance value on the same order of magnitude at frequencies up to four times the Nyquist rate.
Claims8
A digital data line driver comprising:
- (a) a first stage having common mode feedback, the first stage including,
- (i) a class A folded cascode amplifier for providing a majority of the driver's open loop gain, the amplifier having a differential input for receiving a differential input signal, a single-ended common mode feedback input for receiving a common mode feedback voltage and, a differential output,
- (ii) a common mode feedback circuit having a differential input and a single-ended output, the input coupled to the cascode amplifier output and the single-ended output coupled to the cascode amplifier common mode feedback input;
- and
- (b) a second stage having a gain close to unity coupled to the first stage, the second stage including,
- (i) a pair of identical driver circuit, each circuit comprising a pair of error amplifiers having their inverting inputs coupled together and their non-inverting inputs coupled together and each having a single-ended output, each pair of non-inverting inputs being respectively coupled to the differential output of the first stage, and
- (ii) a class AB push-pull complimentary transistor output circuit, coupled to and driven by the single-ended outputs of the driver circuits, the output circuit being coupled back to the inverting inputs so as to provide a second stage gain close to unity.
A digital data line driver suitable for use in a Digital Data Service and an Integrated Services Digital Network, the driver comprising:
- (a) a first stage having common mode feedback and providing a large open loop gain, the first stage including a class A folded cascode amplifier having a differential input for receiving signals, a common mode feedback input for receiving a common mode feedback voltage from a common mode feedback circuit, and a differential output, the common mode feedback circuit being coupled between the differential output and a common mode feedback input on the cascode amplifier;
- and
- (b) a second stage having an input coupled to the first stage differential output and having a gain close to unity, the second stage including a push-pull CMOS output with complimentary error amplifier feedback for providing a high current and a wide voltage swing output while maintaining suitable performance without common mode feedback circuitry.
Dependencies are inferred from the claim text.