U.S. Philips Corporation

Pieter P Vorenkamp

Johannes P Verdaasdonk

Rudy J Van De Plassche

Marcellinus J Pelgrom

Richard Morisson

Arnoldus G Venes

The odd harmonic distortion components in the output signal of a capacitively loaded follower transistor is reduced by means of an additional transistor inserted between the emitter of the follower transistor and the bias current source of the follower transistor. A second follower transistor receives the same input signal as the follower transistor and has its emitter coupled to the emitter of the additional transistor via a compensation capacitor. The current through the compensation capacitor is added to the output current and compensates for the odd harmonic distortion.

Distortion compensation for a capacitively loaded follower

In a folding A/D converter, a comparison part CPM provides a plurality of comparison signals Sc1 . . . Sc9 in response to an input signal Si. The transients in the comparison signals Sc1 . . . Sc9 are mutually shifted and substantially overlap. Because of the overlap, only a relatively small input signal variation is needed to pass all the transients. A limiting part LIM effectively selects portions of the transients. A combining part CBM effectively multiplexes these selected portions into a folding signal Sf. The selection by the limiting part LIM prevents distortion of the folding signal Sf, despite the overlap.

Folding A/D converter

An A/D converter in which an interpolation circuit (15, 16, 17, 18) makes weighted combinations of reference crossing signals (A/Ac,B/Bc) provided by an input circuit (100, 200), so as to obtain an expanded set of reference crossing signals (A/Ac+A1/Ac1 . . . A7/Ac7, B/Bc+B1/Bc1 . . . Bc7). The interpolation circuit (15, 16, 17, 18) is arranged to make at least one weighted combination of reference crossing signals with weighting factors which have a non-integer ratio so as to compensate for a non-linearity in the reference crossing signals (A/Ac,B/Bc). Accordingly, a better compromise is obtained between accuracy, on the one hand, and circuit complexity, on the other hand.

A/D converter with interpolation

An A/D converter has an input part IS which provides differential transitions T1 . . . T.sub.x associated with different levels of an analog input signal. An intermediate part IMS of the converter carries out folding operations and interpolation operations on the transitions to thereby obtain a set of bit-determining signals XO . . . XQ. At least one of the folding and interpolation operations is carried out more than once in alternation with the other of such operations. An output part OS produces a digital output signal from the bit-determining signals. Such an A/D converter can be implemented in a cost-efficient manner and may be combined with digital signal processing circuitry. The repetition of at least one of the operations alternately with the other permits the interpolation factor to be increased without necessitating increased complexity of the output part, and the folding factor to be increased without adversely affecting the accuracy of the converter.

A/D conversion with folding and interpolation

A differential amplifier comprises two input transistors and two cross-coupled transistors arranged in a translinear loop. A difference voltage across a resistance connected between the emitters of the cross-coupled transistors is equal to a difference voltage across the input terminals plus the sum of the offset voltages across resistors arranged in series with the respective emitters of the input transistors. The difference current through the cross-coupled transistors is replicated in output transistors, thereby producing an output signal amplitude larger than the input signal amplitude across a resistance coupled between the emitters of the output transistors. The differential amplifier is suitable, inter alia, as an interpolating residue signal amplifier with additional underflow and overflow ranges in multi-step dual-residue analog-to-digital converters.

Differential amplifier with signal-dependent offset, and multi-step

A differential voltage-current converter has two input transistors and two cross-coupled transistors arranged in a translinear loop, the difference voltage across the emitter resistors of the cross-coupled transistors being equal to the difference voltage across the input terminals. The difference current through the cross-coupled transistors is replicated in the output transistors, thereby enabling a larger output signal amplitude to be obtained. In order to increase the permissible input voltage the bases of the cross-coupled transistors are coupled to the input transistors via emitter-followers. By connecting the collectors of the emitter-followers to the collectors of the output transistors a compensation is obtained for the decreasing current gain at high frequencies.

Voltage-current converter

A sub-ranging analog-to-digital converter includes, in cascade, a coarse converter, a digital-to-analog converter, a subtracter circuit and a fine converter. Errors of the coarse converter are detected in the fine converter by means of an overflow detector and an underflow detector which generate an overflow signal (OF) and an underflow signal (UF), respectively. The digital output (D.sub.A) of the coarse converter is corrected by first subtracting one LBS in a decoder and then, in response to the overflow and underflow signal, adding thereto zero, one or two LBSs.

Multistep analog-to-digital converter with error correction

A track-and-hold circuit includes an input stage (IS), an output stage (OS) and a switching stage (SS). The switching stage is coupled between the input stage and the output stage. The switching stage includes a switching transistor (T10), a differential amplifier (T11/T12), a current source (T13/R11), and a capacitor (C11). In order to improve the frequency response, the input stage is provided with a passive impedance coupled between a base of the switching transistor and a first supply terminal (1) and the input stage is adapted to supply a signal current to the base of the switching transistor. This signal current is related to an input signal applied to the input stage. The output stage includes a first output transistor (T14), a first current source (T15) switched by a tracking signal (Vt), a second output transistor (T16), and a second current source.

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Eindhoven, Netherlands

Pieter P Vorenkamp