Texas Instruments Corporation

Maher Mahmoud Sarraj

Haydar Bilhan

Eric G Soenen

In described examples, a sample and hold circuit is configured to periodically connect one input of an op-amp to a reference voltage through a switch while a second input of the op-amp is connected to an output of the op-amp. Offset cancellation is performed by storing a sampled offset on a sampling capacitor coupled to the second input of the op-amp.

Differential converter with offset cancelation

An analog to digital converter includes leakage current correction circuitry to cancel leakage current injected by a reset switch employing a dummy PMOS switch with a shape factor substantially similar to that of the reset switch. An operational amplifier replicates the voltage of the comparator sense input node to the drain of the dummy transistor to create the same operating point as the reset switch. The resulting leakage current is then repeated and fed back to the node to cancel the offending leakage current.

Analog to digital converter with leakage current correction circuit

A successive approximation register switched capacitor analog to digital converter utilizes a high frequency clock for controlling comparator reset switches and a clock distribution block to operate at lower sample rates. The successive approximation cycles are clocked with the high frequency clock so that the reset switches stay within the leakage limit irrespective of the sample rate but the end of conversion signal is delayed to mimic the slower sample rate.

System and method of clocking low sample rate analog to digital converters while minimizing linearity errors

This invention is a clamp circuit for a video input. The clamp circuit includes: a coupling capacitor; a differential amplifier comparing a video input to predetermined reference voltage; a clamp transistor having a gate connected to the output terminal of the differential amplifier and a source-drain path connected between a power supply voltage and a second terminal; a resistive element connecting the second terminal of the clamp transistor and the coupling capacitor; a first current sink carrying a first predetermined current from the coupling capacitor to ground; and a second current sink carrying a second predetermined current from the second terminal of the said clamp transistor to ground. The resistive element can be a transistor, a resistor, a diode or a switch.

AC clamp circuit for video applications

A buffered bootstrapped input switch employs cancelled charge sharing for use in high performance sample and hold switched capacitor circuits especially useful for implementing, for example, an analog-to-digital converter (ADC) or amplifier circuit front end sampling network, among others. A scheme is employed for estimating the charge loss from the bootstrapping capacitor to the gate of the bootstrapped input switch, storing the estimated charge loss on a small capacitor, buffering the small capacitor, and then adding the estimated charge loss in series to the bootstrap capacitor, to provide an almost ideal bootstrap network.

Buffered bootstrapped input switch with cancelled charge sharing for use in high performance sample and hold switched capacitor circuits

A sample and hold circuit includes an operational amplifier and a plurality of switched capacitors, the switched capacitors introducing a closed loop gain of one-half for the operational amplifier.

Sample and hold circuit

A pipelined analog-to-digital converter is disclosed having a plurality of sample and hold converter stages, each having an interstage amplifier (28) associated therewith. This is a differential amplifier that is implemented without common-mode feedback. The sample and hold stage operates on a reset phase and a gain/DAC phase, wherein the output of the reconstructive DAC is summed with the input to the amplifier (28). A differential input amplifier (60) has the inputs thereof set to common-mode input voltage with a feedback capacitor biased to a common-mode output bias point. During the gain/DAC phase, the bias input is removed and the feedback capacitor connected across the input/output of the amplifier (60). This effectively establishes the common-mode bias points for use by the amplifier (60) during the gain/DAC phase. Further, the differential inputs of the amplifier (60) are connected to one side of respective sampling capacitors, the other side thereof connected through a respective switch to the differential inputs. During the reset phase the input voltage is sampled onto the capacitors and, during the gain/DAC phase, the gates of the capacitors are connected together to remove any common-mode voltage from the input prior to being input to the amplifier (60).

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Plano, TX, United States of America

Maher Mahmoud Sarraj