Analog Devices,inc.

Analog Devices International Unlimited Company

Analog Devices Global Unlimited Company

Siddharth Devarajan

Lawrence A Singer

Hajime Shibata

Trevor Clifford Caldwell

Brian Holford

Gabriele Manganaro

Carroll Clifton Speir

Eric Otte

Nevena Rakuljic

Prawal Man Shrestha

Athanasios Ramkaj

Filip Tavernier

Pingli Huang

Front-end circuitry is difficult to design for high sample rate, wide bandwidth receivers with high performance requirements on noise and linearity. One exemplary front-end circuitry is integrated on-chip with the RF ADC in a receiver, and the circuitry implements ESD protection, attenuation, and gain. The circuitry includes a multi-tap filter with LC circuits, and the filter implements a highly linear filter. Advantageously, the capacitors in the LC circuits are also used for ESD protection. Additionally, tunable attenuator cells are implemented across the multi-tap filter to provide a wide range of variable attenuation. The circuitry can further include a fixed or variable gain stage at the output. The resulting circuitry offers variable gain and attenuation while meeting bandwidth, noise, and linearity requirements.

Front-end for receivers with RF sampling ADCS

A continuous-time sampler has series-connected delay lines with intermediate output taps between the delay lines. Signal from an output tap can be buffered by an optional voltage buffer for performance. A corresponding controlled switch is provided with each output tap to connect the output tap to an output of the continuous-time sampler. The delay lines store a continuous-time input signal waveform within the propagation delays. Controlling the switches corresponding to the output taps with pulses that match the propagation delays can yield a same input signal value at the output. The continuous-time sampler effectively 'holds' or provides the input signal value at the output for further processing without requiring switched-capacitor circuits that sample the input signal value onto some capacitor. In some cases, the continuous-time sampler can be a recursively-connected delay line. The continuous-time sampler can be used as the front end sampler in a variety of analog-to-digital converters.

Continuous-time sampler circuits

The trend in wireless communication receivers is to capture more and more bandwidth to support higher throughput, and to directly sample the radio frequency (RF) signal to enable re-configurability and lower cost. Other applications like instrumentation also demand the ability to digitize wide bandwidth RF signals. These applications benefit from input circuitry which can perform well with high speed, wide bandwidth RF signals. An input buffer and bootstrapped switch are designed to service such applications, and can be implemented in 28 nm complementary metal-oxide (CMOS) technology.

Bootstrapped switching circuit

A time-interleaved analog-to-digital converter (ADC) uses M analog-to-digital converters to sample an analog input signal to produce digital outputs. The M ADCs, operating in a time-interleaved fashion, can increase the sampling speed several times compared to the sampling speed of just one ADC. The time-interleaved ADC can be programmed and reconfigured to trade one performance metric for another. For example, more time can be given to comparator to improve bit error rate or more time can be given to an amplifier for improved settling which improves SNR, SFDR etc. If the time-interleaved converters are randomized, then the amount of 'color' in the noise floor shape can also be traded for other performance metrics.

Time-interleaved ADCs with programmable phases

An apparatus and method for implementing a bootstrapped switching circuit having improved (i.e. faster) turn-on time is provided. In an embodiment, an inner switching loop is implemented in a bootstrapped switching circuit where the inner switching loop is configured to turn on an input switch in the bootstrapped drive circuit independent of the drive circuit output. The embodiment decouples the inner switching loop circuitry from the output drive circuit of the bootstrapped switching circuit, which typically has a larger load capacitance than the inner switching loop. This allows the inner switching loop to turn on the input switch in the bootstrapped switching circuit faster and decreases the turn-on time of the bootstrapped switching circuit.

Bootstrapped switching circuit with fast turn-on

Analog-to-digital converters (ADCs) can have errors which can affect their performance. To improve the performance, many techniques have been used to compensate or correct for the errors. When the ADCs are being implemented with sub-micron technology, ADCs can be readily and easily equipped with an on-chip microprocessor for performing a variety of digital functions. The on-chip microprocessor and any suitable digital circuitry can implement functions for reducing those errors, enabling certain undesirable artifacts to be reduced, and providing a flexible platform for a highly configurable ADC. The on-chip microprocessor is particularly useful for a randomized time-interleaved ADC. Moreover, a randomly sampling ADC can be added in parallel to a main ADC for calibration purposes. Furthermore, the overall system can include an efficient implementation for correcting errors in an ADC.

Randomly sampling reference ADC for calibration

A time-interleaved analog-to-digital converter (ADC) uses M sub-analog-to-digital converters (sub-ADCs) to, according to a sequence, sample an analog input signal to produce digital outputs. When the M sub-ADCs are interleaved, the digital outputs exhibit mismatch errors between the M sub-ADCs due to mismatches between the sub-ADCs. A more second order subtle effect is that the mismatch error for a particular digital output from a particular ADC, due to internal coupling or other such interaction and effects between the M sub-ADCs, can vary depending on which sub-ADC(s) were used before and/or after the particular sub-ADC. If M sub-ADCs are time-interleaved randomly, the mismatches between the M sub-ADCs become a function of the sub-ADC selection pattern in the sequence. The present disclosure describes mechanisms for measuring and reducing these order-dependent mismatches to achieve high dynamic range performance in the time-interleaved ADC.

Methods and systems for reducing order-dependent mismatch errors in time-interleaved analog-to-digital converters

In one example embodiment, a programmable capacitor array is provided for low distortion and minimizing linearity degradation of an input (Vin) by utilizing control circuitry to switch on and off an array of MOSFET switches. The control circuitry turns on a MOSFET to load a capacitance on Vin and turns off the MOSFET to remove the capacitance from Vin in response to a Din control signal. When the intention is to load Vin with the capacitance, the MOSFET is left on continuously. When the intention is to remove or unload the capacitance from Vin, the MOSFET is primarily turned off, however, the MOSFET is still periodically turned on with appropriate voltage levels in response to a clock signal for periods of time when the loading of the capacitance on Vin is tolerable to the system, thereby ensuring minimal linearity degradation of Vin due to the programmable capacitor array system.

Low-distortion programmable capacitor array

An example apparatus, system, and method for sampling in an interleaved sampling circuit having multiple channels. In an embodiment, an input clock is used to synchronize the transitions of sampling clocks from a first to second voltage level, relative to one another. The sampling clocks are input to a sampling circuit. The input clock switches a common switch that pulls each sampling clock to the second voltage level through a common path on input clock transitions from a first to a second clock state. The transition from the first to a second voltage level of each sampling clock triggers a sample taken on one of the channels. The first voltage level may be boosted to drive switches on in the sampling circuit. Synchronizing transitions of the outputs through the common switch and common path reduces timing mismatch between the sampling clocks controlling the channels.

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Arlington, MA, United States of America

Siddharth Devarajan