Caelus Technologies Limited

Hong Kong Applied Science and Technology Research Institute Company, Limited

Chi Fung Lok

Xiaoyong He

Zhi Jun Li

Shiyuan Zheng

Le Feng Shen

An interleaved Analog-to-Digital Converter (ADC) has a reference channel receiving an attenuated analog input. The reference channel is also calibrated to remove capacitor-ratio mismatch, static, and dynamic mismatches and produces a linear replica of the data channels with negligible nonlinear errors due to attenuation. Nonlinear errors on the data channels are corrected by Harmonic Distortion HD2 and HD3 coefficients. A counter increments when the sign bit of a nonlinear-corrected channel code is negative. The count is doubled and reduced by a number of samples to generate a HD2 cost function that adjusts the HD2 coefficient in a LMS loop. A HD3 correlation is generated by multiplying the reference channel output by its difference with the nonlinear-corrected channel code. The sign of the correlation code increments a second counter which generates a HD3 cost function whose sign bit adjusts the HD3 coefficient. These 2 counters generate cost functions, eliminating sample storage.

Analog-to-digital converter (ADC) with reference ADC path receiving attenuated input to generate error codes for second and third harmonics by counting negative and positive codes

A multi-stage pipelined Analog-to-Digital Converter (ADC) has an offset correction circuit embedded in the residue amplifier between stages. The offset corrector has a low-pass filter that filters the output of the residue amplifier, and the filtered offset is amplified and stored on an offset capacitor during an autozeroing phase of the residue amplifier. During an amplify phase of the residue amplifier, switches disconnect the amplifier from the offset capacitor and instead ground the input of the offset capacitor, and other switches connect the output terminal of the offset capacitor to the input of the residue amplifier. The offset stored on the offset capacitor is combined with the residue voltage from the first ADC stage's capacitor array and applied to an input of the residue amplifier to effectively subtract the detected offset. Two offset capacitors and sets of switches can be used to implement a differential offset corrector.

Discrete-time offset correction circuit embedded in a residue amplifier in a pipelined analog-to-digital converter (ADC)

A reference buffer has many legs each with an upper transistor, a lower transistor, and a resistor or current source as a tail device in series. The source or emitter of the upper (lower) transistor generates an upper (lower) reference voltage. This source follower transistor configuration has a low output impedance and high current. The gate or base of the upper (lower) transistors are driven by a first (second) control node. A control leg has an upper transistor, a lower transistor, and a tail device in series. The source and gate, or emitter and base, are connected together for the upper and lower transistors and generate the upper and lower control nodes. Alternately, the gate or base of the upper (lower) transistor is driven by an op amp receiving an upper (lower) bandgap voltage and the upper (lower) control node as negative feedback.

Cascode Class-A differential reference buffer using source followers for a multi-channel interleaved Analog-to-Digital Converter (ADC)

A differential residue amplifier fits between Analog-to-Digital Converter (ADC) stages. Switched-Capacitor Common-Mode Feedback circuits determine voltage shifts. An AC-coupled input network uses switched capacitors to shift upward voltages of the differential inputs to the residue amplifier to apply to an upper pair of p-channel differential transistors with sources connected to the power supply. The AC-coupled input network also shifts downward in voltage the differential inputs to the residue amplifier to apply to a lower pair of n-channel differential transistors with grounded sources. The drains of the p-channel differential transistors connect to differential outputs through p-channel cascode transistors. N-channel cascode transistors connect the drains of the n-channel differential transistors to the differential outputs. The drains of differential transistors can be input to differential amplifiers to drive the gates of the cascode transistors for gain boosting. No tail current is used, allowing for wider output-voltage swings with low supply voltages.

Gain-boosted class-AB differential residue amplifier in a pipelined Analog-to-Digital Converter (ADC) using switched-capacitor common-mode feedback to eliminate tail current sources

An N-channel interleaved Analog-to-Digital Converter (ADC) has a variable delay added to each ADC's input sampling clock. The variable delays are each programmed by a Successive-Approximation-Register (SAR) during calibration to minimize timing skews between channels. Each channel receives a sampling clock with a different phase delay. The sampling clocks are overlapping multi-phase clocks rather than non-overlapping. Overlapping the multi-phase clocks allows the sampling pulse width to be enlarged, providing more time for the sampling switch to remain open and allow analog voltages to equalize through the sampling switch. Higher sampling-clock frequencies are possible than when non-overlapping clocks are used. The sampling clock is boosted in voltage by a bootstrap driver to increase the gate voltage on the sampling switch, reducing the ON resistance. Sampling clock and component timing skews are reduced to one LSB among all N channels.

Multi-channel interleaved analog-to-digital converter (ADC) using overlapping multi-phase clocks with SAR-searched input-clock delay adjustments and background offset and gain correction

An N-channel interleaved Analog-to-Digital Converter (ADC) has a variable delay added to each ADC's input sampling clock. The variable delays are each programmed by a Successive-Approximation-Register (SAR) during calibration to minimize timing skews between channels. In each channel the ADC output is filtered, and a product derivative correlator generates a product derivative factor for correlation to two adjacent ADC channels. A matrix processor arranges the product derivative factors from the product derivative correlators into a matrix that is multiplied by a correlation matrix. The correlation matrix is a constant generated from an N&#xd7;N shift matrix. The matrix processor outputs a sign-bit vector. Each bit in the sign-bit vector determines when tested SAR bits are set or cleared to adjust a channel's variable delay. Sampling clock and component timing skews are reduced to one LSB among all N channels.

Matrix processor generating SAR-searched input delay adjustments to calibrate timing skews in a multi-channel interleaved analog-to-digital converter (ADC)

An N-channel interleaved Analog-to-Digital Converter (ADC) has a variable delay added to each ADC's input sampling clock. The variable delays are each programmed by a Successive-Approximation-Register (SAR) during calibration to minimize timing skews between channels. An auto-correlator generates a sign of a correlation error for a pair of ADC digital outputs. SAR bits are tested with the correlation sign bit determining when to add or subtract SAR bits. First all pairs are calibrated in a first level of a binary tree of mux-correlators. Then skews between remote pairs and groups are calibrated in upper levels of the binary tree using auto-correlators with inputs muxed from groups of ADC outputs input to the binary tree of mux-correlators. The binary tree of mux-correlators can include bypasses for odd and non-binary values of N. Sampling clock and component timing skews are reduced to one LSB among both adjacent channels and remote channels.

Calibration of timing skews in a multi-channel interleaved analog- to-digital converter (ADC) by auto-correlation of muxed-together channels in binary output tree

A first calibration measures capacitor array mis-match and updates a Look-Up Table (LUT) with calibrated weights that are copied to both a positive LUT and a negative LUT, and then adjusted for non-linearity errors by a second calibration using a Least Mean-Square (LMS) method. The binary code in the Successive-Approximation Register (SAR) is complemented to generate a complement code with a sign bit. When the sign bit is positive, entries for complement code bits=1 are read from the positive LUT and summed, a first offset added, and the sum normalized to get a corrected code. When the sign bit is negative, entries for complement code bits=0 are read from the negative LUT and summed, a second offset added, and the sum normalized to get the corrected code. A Multi-Variable Stochastic Gradient Descent method generates polynomial coefficients that further correct the corrected code.

Calibration of residual errors using least-mean-squares (LMS) and stochastic-gradient methods for an analog-to-digital converter (ADC) with a pre-calibrated lookup table

A self-calibrating Analog-to-Digital Converter (ADC) performs radix error calibration using a Successive-Approximation Register (SAR) to drive test voltages onto lower-significant capacitors. The final SAR code is corrected by performing LSB averaging on LSB averaging capacitors and then accumulated, and the measurement repeated many times to obtain a digital average measurement. An ideal radix or ratio of the measured capacitor's capacitance to a unit capacitance of an LSB capacitor is subtracted from the digital average measurement to obtain a measured error that is stored in a Look-Up Table (LUT) with the ideal radix. Radix error calibration is repeated for other capacitors to populate the LUT. During normal ADC conversion, the SAR code obtained from converting the analog input is applied to addresses the LUT, and all ideal radixes and measured errors for 1 bits in the SAR code are added together to generate an error-corrected digital value.

Calibration of radix errors using Least-Significant-Bit (LSB) averaging in a Successive-Approximation Register Analog-Digital Converter (SAR-ADC) during a fully self-calibrating routine

A multi-stage Successive-Approximation Register (SAR) pipeline Analog-to-Digital Converter (ADC) has an amplifier between two switched capacitor networks, each controlled by a SAR. The load capacitance of the amplifier is magnified due to the amplifier's gain. This magnified load capacitance can disproportionately increase power consumption. The back plates of the second-stage switched capacitors are connected to the amplifier input using a feedback switch during an amplification phase, so that the second-stage switched capacitors are connected between the input and output of the amplifier as a feedback capacitor, rather than a load capacitor. Reset switches are added to drive both plates of the second-stage switched capacitors to ground during a reset phase before the amplification phase. Thus the second-stage switched capacitors function as both the feedback capacitor and as the switched capacitors controlled by the second SAR. Amplifier power is reduced since there is no separate load capacitor during the amplification phase.

Loading-free multi-stage SAR-assisted pipeline ADC that eliminates amplifier load by re-using second-stage switched capacitors as amplifier feedback capacitor

A circuit and method for a bandgap voltage reference operating at 1 volt or below is disclosed, wherein the operational amplifier (A) drives resistors (R, R) only so that both the flicker noise contribution and the process sensitivity due to the conventional metal oxide semiconductor (MOS) devices used as a current mirror within the proportional-to-absolute-temperature (PTAT) loop are eliminated. Two symmetric resistive divider pairs formed by (R/R, R/RB) are inserted to scale down both the base-emitter voltages (V, V) of bipolar transistors (Q, Q) and the PTAT current (I) so that an output reference voltage (V) becomes scalable. Proper bias currents through transistors (M, M), which are used to bias (Q, Q) and (R/R, R/R) respectively, are produced by an additional V-I converter () using Vitself, resulting in a final process, voltage and temperature (PVT) insensitive output reference voltage.

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Chi Fung Lok