Systems and methods relating to analog-to-digital converters. A delay block receives an input signal at the same time as a coarse ADC (CADC) block. The CADC block produces a multi-bit output and this output is applied to a signal processing block. The delay block delays the input signal from being applied to the signal processing block until the output of the CADC block has been applied/configures the signal processing block. The signal processing block may be a signal shifter, the output of which is ultimately applied to a fine ADC (FADC) block. In an alternative, the signal processing block may be the FADC block. Regardless of the configuration, the output of the CADC is delayed until the output of the FADC block is available. The outputs of the CADC and the FADC blocks are then simultaneously applied to an encoder that produces the overall system output.

An image sensor is proposed to have a stack with at least a pixel array tier and a control logic tier. The pixel array tier comprises an array of pixels which are arranged into pixel columns n, each pixel column n comprising a number of N sub-columns: Each sub-column is denoted by N(n,i) with 1iN. The control logic tier comprises an array of analog-to-digital-converters which are arranged into ADC columns m, wherein each analog-to-digital converter comprises a number of M stages. Each stage is denoted by M(m,j) with 1jM, Furthermore, each respective sub-column N(n,i) is electrically connected to a dedicated stage M(m,j=i) and the stages M(m,j) are electrically interconnected to form the analog-to-digital converters, respectively. The control logic tier is arranged to sequentially read out the sub-columns N(n,i), wherein the stages M(m,j=i) dedicated to the sub-columns N(n,i) are arranged as input stages to sequentially receive signal levels of the pixels in the sub-columns N(n,i), respectively. The input stages are arranged to perform on the sequentially received signal levels a coarse first analog-to-digital conversion. The remaining stages M(m,ji) are arranged to sequentially perform finer analog-to-digital conversions of the received signal levels.

An analog-to-digital converter (ADC) includes a first ADC stage with a first sub-ADC stage configured to output a first digital value corresponding to an analog input voltage. A current steering DAC stage is configured to convert the analog input voltage and the first digital value to respective first and second current signals, determine a residue current signal representing a difference between the first current signal and the second current signal in the current domain, and convert the residue current signal to an analog residual voltage signal. A second ADC stage is coupled to the first ADC stage to receive the analog residual voltage signal, and convert the analog residue voltage signal to a second digital value. An alignment and digital error correction stage is configured to combine the first and the second digital values into a digital output voltage.

A receiver includes a variable resolution analog-to-digital converter (ADC) and variable resolution processing logic/circuitry. The processing logic may use feed-forward equalization (FFE) techniques to process the outputs from the ADC. When receiving data from a channel having low attenuation, distortion, and/or noise, the ADC and processing logic may be configured to sample and process the received signal using fewer bits, and therefore less logic, than when configured to receiving data from a channel having a higher attenuation, distortion, and/or noise. Thus, the number of (valid) bits output by the ADC, and subsequently processed (e.g., for FFE equalization) can be reduced when a receiver of this type is coupled to a low loss channel. These reductions can reduce power consumption when compared to operating the receiver using the full (i.e., maximum) number of bits the ADC and processing logic is capable of processing.

A clock-less delay comparator coupled to a first input signal and a second input signal, the clock-less delay comparator comprising: a first transistor having a control terminal coupled to the second input signal, a first current terminal coupled to a first voltage supply, and a second current terminal; a second transistor having a control terminal, a first current terminal coupled to the first voltage supply, and a second current terminal; a third transistor having a control terminal, a first current terminal coupled to the first voltage supply, and a second current terminal; a fourth transistor having a control terminal coupled to the first input signal, a first current terminal coupled to the first voltage supply, and a second current terminal; a fifth transistor having a control terminal coupled to the second input signal, a first current terminal, and a second current terminal coupled to the control terminal of the third transistor; a sixth transistor having a control terminal coupled to the first input signal, a first current terminal, and a second current terminal coupled to the control terminal of the second transistor and the second current terminal of the third transistor; a seventh transistor having a control terminal coupled to the control terminal of the second transistor, a first current terminal coupled to a second voltage supply, and a second current terminal coupled to the first current terminal of the fifth transistor; an eighth transistor having a control terminal coupled to the control terminal of the third transistor, a first current terminal coupled to the second voltage supply, and a second current terminal coupled to the first current terminal of the sixth transistor; a ninth transistor having a control terminal coupled to the first input signal, a first current terminal coupled to the second current terminal of the first transistor, and a second current terminal coupled to the second current terminal of the second transistor and the second current terminal of the fifth transistor; and a tenth transistor having a control terminal coupled to the second input signal, a first current terminal coupled to the second terminal of the fourth transistor, and a second current terminal coupled to the second current terminal of the third transistor.

The present disclosure provides alternative solutions to the problem of providing a stable voltage reference to high speed ADCs that possess high sampling rates. In one example the high speed amplifier is replaced by a smaller, slower, lower power amplifier in combination with a relatively large capacitor connected to the same node as the amplifier output and the ADC reference input. The capacitor is charged substantially to the external reference voltage and hence keeps the reference input of the ADC almost at the external reference voltage between conversions, such that when conversion is about to occur and the external reference is switched in then very little charge is required from the external reference, and hence the reference signal quickly settles. An alternative arrangement is to replace the amplifier with a comparator that takes as one of its inputs the external reference signal, and as the other of its inputs the internal reference to the ADC, and makes use of a control circuit that adjusts the threshold of the comparator from bit-trial to bit-trial until the internal reference is brought up to substantially the same signal level as the external reference. When the external reference is then switched in to supply the ADC circuit it settles very quickly and draws very little power therefrom.

A multi-stage analog-to-digital converter (ADC) suitable for low power applications, such as glucose monitoring, may be required to digitize a slow-moving signal. As such, a multi-stage ADC must be versatile. Accordingly, the multi-stage ADC can be configured to operate at different bandwidths and resolutions through the use of ADC stages that can be enabled or disabled in an exchange between resolution and speed. Each ADC stage digitizes an input signal (e.g., a voltage or a current) using an analog comparison to access a lookup table for a digital signal that represents the input signal at a particular accuracy. Unlike other multi-stage approaches, the digitization is asynchronous (i.e., requires no clock) and can provide simplicity, speed, and low-power operation to the multi-stage ADC.

An input signal Vin is sampled, when a first terminal of a sampling capacitor is connected to a node and a second terminal of the sampling capacitor is connected to an analog ground. A charge transfer operation is performed, when the first terminal of the sampling capacitor is connected to the analog ground and the second terminal of the sampling capacitor is connected to an inverting input terminal of an operational amplifier. A quantization is performed, when an output of the operational amplifier is input to a quantizer. Most significant bits are generated by repeating a subtraction operation in which a charge subtraction unit subtracts a charge accumulated in the integration capacitor based on a quantization result a predetermined number of times. Least significant bits are generated when a voltage provided by amplifying a voltage corresponding to a charge remaining in the integration capacitor is input to a sub-A/D converter after generation of the most significant bits. A sum of the most significant bits and the least significant bits are output as an output signal. Initialization of the charge of the integration capacitor, the charge transfer operation for a next A/D conversion, and generation of the most significant bits are performed in parallel with the A/D conversion in the sub-A/D converter after the generation of the most significant bits.

A circuit includes a voltage-to-time conversion element configured to receive an input voltage at an input and to generate a time domain representation of the input voltage. The voltage-to-time conversion element includes an amplifier having an amplifier input coupled to the input, a zero crossing detector coupled to an output of the amplifier, and a current source selectively coupled to the amplifier input by way of a switching element.

According to an aspect, a tri-level digital to analog converter (DAC) comprises a first set of switches turned on to cause a first analog value with a first error as an output for a first digital value, a second set of switches turned on to cause a second analog value with a second error as the output for a second digital value, wherein, both the first set of switches and the second set of switches are turned on to cause a third analog value, proportional to the first error and the second error, as the output for a digital value equal to zero, and both the first set of switches and the second set of switches are turned off to cause a fourth analog value equal to zero as the output for a fourth digital value representing a reset state.