Differential sample-and-hold circuit
First Claim
1. A monolithic differential sample-and-hold circuit, comprising:
- a preamplifier for processing an analog input signal and providing corresponding differential analog signals;
a first differential amplifier connected to receive the analog signals from said preamplifier to provide a first amplified differential analog signal;
a second differential amplifier also connected to receive the analog signals from said preamplifier, to provide a second amplified differential analog signal identical to said first amplified differential analog signal;
two capacitors, each having a grounded terminal and an ungrounded terminal;
a first pair of diodes having anode terminals connected to receive said first amplified differential analog signal, and cathode terminals each connected to said ungrounded terminal of a different one of said capacitors;
a second pair of diodes having cathode terminals connected to receive said second differential analog signal and anode terminals connected to corresponding cathode terminals of said first pair of diodes;
a post-amplifier having differential inputs connected to said ungrounded terminals of said capacitors; and
a bias signal source connectable to said first and second pairs of diodes to provide forward bias in response to a tracking-mode signal and reverse bias in response to a hold-mode signal;
whereby said first and second pairs of diodes are forward-biased in response to the tracking-mode signal, to allow said first and second amplified differential analog signals to be coupled through said first and second pairs of diodes to said capacitors, and are reverse-biased in response to the hold-mode signal, to isolate said capacitors from said analog signals.
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Accused Products
Abstract
A high-speed sample-and-hold circuit well suited for fabrication in monolithic form, the circuit including a pair of capacitors used to track a differential analog signal, and at least two switches for connecting the analog signal to the capacitors in a tracking mode, and for isolating the capacitors from the analog signal in a hold mode. In a preferred embodiment of the invention, the switches are diodes and each capacitor is driven differentially through a separate pair of diodes, which are forward-biased in the tracking mode and reverse-biased in the hold mode. Additional circuitry is provided to compensate for variations in characteristics of the diodes due to temperature changes. Furthermore, the effects of capacitive coupling through the diodes in the hold mode are minimized by disconnecting the analog input signal and substituting a signal derived from the held signal stored in the capacitors.
166 Citations
8 Claims
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1. A monolithic differential sample-and-hold circuit, comprising:
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a preamplifier for processing an analog input signal and providing corresponding differential analog signals; a first differential amplifier connected to receive the analog signals from said preamplifier to provide a first amplified differential analog signal; a second differential amplifier also connected to receive the analog signals from said preamplifier, to provide a second amplified differential analog signal identical to said first amplified differential analog signal; two capacitors, each having a grounded terminal and an ungrounded terminal; a first pair of diodes having anode terminals connected to receive said first amplified differential analog signal, and cathode terminals each connected to said ungrounded terminal of a different one of said capacitors; a second pair of diodes having cathode terminals connected to receive said second differential analog signal and anode terminals connected to corresponding cathode terminals of said first pair of diodes; a post-amplifier having differential inputs connected to said ungrounded terminals of said capacitors; and a bias signal source connectable to said first and second pairs of diodes to provide forward bias in response to a tracking-mode signal and reverse bias in response to a hold-mode signal; whereby said first and second pairs of diodes are forward-biased in response to the tracking-mode signal, to allow said first and second amplified differential analog signals to be coupled through said first and second pairs of diodes to said capacitors, and are reverse-biased in response to the hold-mode signal, to isolate said capacitors from said analog signals. - View Dependent Claims (2, 3)
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4. A monolithic differential sample-and-hold circuit comprising:
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a preamplifier for processing an analog input signal and providing corresponding differential analog signals; a first differential amplifier connected to receive the analog signals from said preamplifier to provide a first amplified differential analog signal; a second differential amplifier also connected to receive the analog signals from said preamplifier, to provide a second amplified differential analog signal identical to said first amplified differential analog signal; two capacitors, each having a grounded terminal and an ungrounded terminal; a first pair of diodes having anode terminals connected to receive said first amplified differential analog signal, and cathode terminals each connected to said ungrounded terminal of a different one of said capacitors; a second pair of diodes having cathode terminals connected to receive said second differential analog signal and anode terminals connected to corresponding cathode terminals of said first pair of diodes; a post-amplifier having differential inputs connected to said ungrounded terminals of said capacitors; and
a bias signal source connectable to said first and second pairs of diodes to provide forward bias in response to a tracking-mode signal and reverse bias in response to a hold-mode signal;
said bias signal source including means for maintaining a constant forward-bias current through said diodes when in the tracking mode, in spite of variations in diode characteristics due to temperature changeswhereby said first and second pairs of diodes are forward-biased in response to the tracking-mode signal, to allow said first and second amplified differential analog signals to be coupled through said first and second pairs of diodes to said capacitors, and are reverse-biased in response to the hold-mode signal, to isolate said capacitors from said analog signals. - View Dependent Claims (5)
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6. A differential sample-and-hold circuit comprising:
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input amplifier means providing a differential analog signal; capacitor means; switching means for selectively coupling the differential analog signal to said capacitor means; and output amplifier means having differential inputs supplied from said capacitor means, to provide a sampled analog output signal; and wherein said capacitor means includes two capacitors, each connected between a common point and one of the differential inputs of said output amplifier means, said switching means includes two pairs of diodes, means for forward-biasing said diodes to provide a tracking mode of operation, in which the differential analog signal is coupled to said capacitors, and means for reverse-biasing said diodes to provide a hold mode of operation, in which said capacitors are electrically isolated from the differential analog signal and provide inputs representative of a sampled analog signal to said output amplifier means, and said input amplifier means includes a preamplifier providing a differential analog signal, and two differential amplifiers, each having inputs supplied by said preamplifier, and each supplying a differential pair of outputs to a different one of said pairs of diodes.
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7. A differential sample-and-hold circuit, comprising:
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input amplifier means providing a differential analog signal; capacitor means; switching means for selectively coupling the differential analog signal to said capacitor means; and output amplifier means having differential inputs supplied from said capacitor means, to provide a sampled analog output signal; and wherein said capacitor means includes two capacitors, each connected between a common point and one of the differential inputs of said output amplifier means, said switching means includes at least one pair of diodes, means for forward-biasing said diodes to provide a tracking mode of operation, in which the differential analog signal is coupled to said capacitors, and means for reverse-biasing said diodes to provide a hold mode of operation, in which said capacitors are electrically isolated from the differential analog signal and provide inputs representative of a sampled analog signal to said output amplifier means, and said switching means further includes means operative only in the hold mode, for disconnecting the differential analog signal and substituting a signal derived from said capacitors, to minimize the effect of coupling through said diodes when in the hold mode, the substituted signal being independent of the differential analog signal.
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8. A differential sample-and-hold circuit, comprising:
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input amplifier means providing a differential analog signal; capacitor means; switching means for selectively coupling the differential analog signal to said capacitor means; and output amplifier means having differential inputs supplied from said capacitor means, to provide a sampled analog output signal; and wherein said capacitor means includes two capacitors, each connected between a common point and one of the differential inputs of said output amplifier means, and said switching means includes at least one pair of diodes, means for compensating for changes in conduction characteristics of said diodes due to temperature, means for forward-biasing said diodes to provide a tracking mode of operation, in which the differential analog signal is coupled to said capacitors, and means for reverse-biasing said diodes to provide a hold mode of operation, in which said capacitors are electrically isolated from the differential analog signal and provide inputs representative of a sampled analog signal to said output amplifier means.
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Specification