Gain regulation circuit for an amplifier circuit

Amplifiers – With semiconductor amplifying device – Including differential amplifier

Patent

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

330256, H03F 345, H03G 330

Patent

active

045020183

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to electronic amplifier circuits having a regulatable gain, and in particular to a gain regulation circuit for use in a telephone instrument and whereby the gain of the instrument speech paths may be adjusted e.g. for matching the receiver gain to the line loop impedance.
An electronic telephone instrument includes an amplifying speech path whereby speech signals are relayed from the instrument microphone to the line and from the line to the instrument receiver. It will be appreciated that for optimum performance of the instrument the receiver and transmitter speech paths must each include some means of gain regulation to prevent overloading and to provide matching of the receiver gain to the line impedance. The line or loop impedance is in general proportional to the length of the subscriber loop between the instrument and the exchange and can thus have any value within a clearly defined range. Because it is necessary to cater for a wide variation of loop length, it is essential that the receiver circuit of the subscriber's instrument incorporates provision for line length compensation. To compensate loop length variations many telephone administrations require the provision of receiver circuits that can be set to a gain figure anywhere between upper and lower preset limits.
Furthermore, in order to prevent overloading and consequent saturation of the transmitter output state to the line it is necessary to provide some form of gain control whereby a speech signal waveform may be limited in amplitude. This technique commonly known as soft clipping is described in my co-pending application Ser. No. 491,834, filed May 5, 1983.
A particularly useful variable gain element is the transistor long tailed pair the gain of which can be determined by controlling the common emitter current of the pair. The use of a single long tailed pair is, however, somewhat restricted by its significantly non linear signal/gain characteristic which gives rise to distortion for all but very low signal levels. In some applications this distortion may be outside the limits specified by the telephone administration.


SUMMARY OF THE INVENTION

The object of the present invention is to provide a gain regulation circuit whereby a smooth and continuous gain variation between predefined limits in response to a control signal may be effected.
According to the invention there is provided a signal amplifier element having a controllable gain and comprising a plurality of transistor long tailed pairs, wherein the transistors of the pairs are so constructed that the maxima of the signal/gain characteristics of the pairs are symmetrically disposed about the signal zero level, and wherein the signal/gain characteristic of all the pairs acting in combination includes a substantially constant region.
According to another object of the invention there is provided a gain regulator and signal amplifier circuit e.g. for an electronic telephone subset, the circuit comprising a first long tailed pair of transistors having substantially identical characteristics, and 2n further long tailed pairs of transistors, where n is an integer including unity, wherein corresponding transistors of the 2n further pairs have emitter areas in the ratio 1:a; a:1; where a lies between zero and unity, whereby the gain maxima of the characteristics corresponding to the further long tailed pairs are symmetrically disposed about the signal zero so as to provide together a substantially constant gain region of significantly lower gain than the gain maxima of the first long tailed pair, and wherein the circuit includes control means whereby weighted contributions to the circuit gain characteristic may be provided from the first pair and from the 2n further pairs so as to provide a stage gain adjustable between limits defined by the gain of the first pair and the gain of the 2n further pairs. We have found that by providing an emitter area mismatch between the transistors of a long tailed pair the maxima of the signal/gain cha

REFERENCES:
patent: 3940708 (1976-02-01), Sumi et al.

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Gain regulation circuit for an amplifier circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Gain regulation circuit for an amplifier circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gain regulation circuit for an amplifier circuit will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-518595

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.