US3624414A

US3624414A - Circuit arrangement for polarity reversal of signals from a signal source

Info

Publication number: US3624414A
Application number: US884449A
Authority: US
Inventors: Leonardus Petrus Jozef Va Dijk; Geerlof Jan Korevaar
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1968-12-21
Filing date: 1969-12-12
Publication date: 1971-11-30
Anticipated expiration: 1988-11-30
Also published as: SE352503B; FR2026815A1; AT297096B; DE1960699B2; BE743445A; DE1960699A1; NL6818490A; JPS4928781B1; GB1259719A; CH503428A

Abstract

A polarity reversal arrangement provided with two seriesarranged electronic switching elements, for example, for use in pulse code modulation. freedom In order to satisfy the strict requirements of polarity reversal at the instants of an alternation of polarity of the signals from a signal source and the requirement of freedom from distortion, the polarity reversal arrangement is provided with a bridge composed of resistors wherein the signal source is connected to one end of a diagonal branch of the bridge and wherein the input circuit of an amplifier reversing the polarity of the input signal is connected to the other end of this diagonal branch and wherein the series arrangement of the two electronic switching elements is included between the ends of the other diagonal branch, the junction of the electronic switching elements being connected to the output circuit of the amplifier, while the output signals of the polarity reversal arrangement are derived from one end of the last-mentioned diagonal branch of the bridge.

Description

United States Patent REVERSAL 0F SIGNALS FROM A SIGNAL SOURCE 7 Claims, 2 Drawing Figs.

3,130,325 4/1964 Rubin et a1. 307/229 3,196,291 7/1965 Woodward, .lr. 307/229 3,311,835 3/1967 Richman 328/26 X 3,480,794 11/1969 Richman 307/261 X 3,509,372 4/1970 Bicking 307/236 Primary Examiner-Stanley T. Krawczewicz A!l0rneyFrank R. Trifari ABSTRACT: A polarity reversal arrangement provided with two series-arranged electronic switching elements, for example, for use in pulse code modulation. freedom In order to satisfy the strict requirements of polarity reversal at the instants ofan alternation of polarity of the signals from a signal source and the requirement of freedom from distortion, the polarity reversal arrangement is provided with a bridge composed of resistors wherein the signal source is connected [52] US. Cl 307/262, to one end ofa diagonal branch of the bridge and wherein the 307/229, 307/236, 307/261, 321/8, 328/26, input circuit of an amplifier reversing the polarity of the input 328/140 signal is connected to the other end of this diagonal branch [51 lnt. Cl l-l03k 1/12, and wherein the series arrangement of the two electronic H02m 7/00 switching elements is included between the ends of the other [50] Field of Search 307/229, diagonal branch, the junction of the electronic switching ele- 236, 261, 262; 328/26, 55, 57, 118, 140, 142, 143; ments being connected to the output circuit of the amplifier, 321/8 while the output signals of the polarity reversal arrangement are derived from one end of the last-mentioned diagonal References (med branch of the bridge.

UNITED STATES PATENTS 3,112,449 1 H1963 Miller 328/26 AMPL/F/ER PULSE CODE MODULATOR 19 C I i 7 l7 8 A5 L I ;Z 10 I 7L I d I f i l 5 12 21 i AMPL /F/R 22 CIRCUIT ARRANGEMENT F OR POLARIT Y REVERSAL F SIGNALS F ROM A SIGNAL SOURCE The invention relates to a circuit arrangement for polarity reversal of signals from a signal source, which circuit arrangement is provided with two series-arranged electronic switching elements. Such circuit arrangements for polarity reversal are used inter alia in pulse code modulation transmission devices for generating rectified speech signals by means of polarity reversal, in particular the rectified speech signals thus obtained are applied to a pulse code modulator for generating the pulse code groups to be transmitted which are transferred to the receiver together with a polarity pulse characterizing the polarity of the speech signals to be transmitted.

Special care is to be bestowed on the construction of such circuit arrangements for polarity reversal. In fact, on the one hand it should be ensured that the polarity reversal takes place exactly at the instants of change of polarity of the speech signals, since as has been found from extensive investigations already small deviations from these instants for polarity reversal are disturbingly noticeable in the reproduction of the transmitted speech signals. On the other hand distortions and influences by disturbing effects such as, for example, temperature effects, direct current drift phenomena etc. are to be avoided.

It is an object of the present invention to provide a circuit arrangement of the type described in the preamble which is simple and convenient in construction, and in which the above-mentioned requirements for polarity reversal are satisfied, while this circuit arrangement is furthermore distinguished by its wide possibilities of use.

According to the invention the circuit arrangement for polarity reversal is provided with a bridge composed of resistors, the signal sourcebeing connected to one end of a diagonal branch of the bridge and the input circuit of an amplifier which reverses the polarity of the input signal being connected to the other end of this diagonal branch, the series arrangement of the two electronic switching elements being included between the ends of the other diagonal branch, the junction of the electronic switching elements being connected to the output circuit of the amplifier while the output signals of the polarity reversal arrangement are derived from one end of the last-mentioned diagonal branch of the bridge.

In order that the invention may be readily carried into effect, a few embodiments thereof will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawing, in which FIG. I shows a circuit arrangement for polarity reversal according to the invention, while FIG. 2 shows a modification of the circuit FIG. 1.

The circuit arrangement shown in FIG. I for polarity reversal according to the invention is intended for generating rectified signals by means of polarity reversal in the band of 0.3--l0 kHz., which signals originate from a signal source including output terminals 2, 3 and an internal resistor 4, the output terminal 2 of said source being connected to a point of fixed potential, for example, earth potential, and the other output terminal 3 of the source being connected to the input circuit of the circuit arrangement which for the purpose of polarity reversal of the signals from the signal source 1 is provided with two series-arranged electronic switching elements 5, 6 in the form of diodes. The output signals of the circuit arrangement are applied for handling in a user 7, for example, a pulse code modulator to an amplifier 8 having a high input resistance.

In order to satisfy the strict requirements of polarity reversal at the instants of an alternation of polarity of the signals from the signal source 1 and the requirements of freedom from distortion, the polarity reversal arrangement according to the invention is provided with a bridge composed of

resistors

9, 10, 11, 12, the signal source 1 being connected to one end 13 of a diagonal branch of the bridge and the input circuit of an amplifier I5, which reverses the polarity of the input signal,

arrangement of being connected to the other end 14 of this diagonal branch the series arrangement of the two diodes 5, 6, being included between the

ends

16, 17 of the other diagonal branch, the junction of the diodes 5, 6 being connected to the output circuit of the amplifier 15, while the output signals of the polarity reversal arrangement are derived from the end 17 of the lastmentioned diagonal branch of the bridge. In the embodiment shown the amplitude of each

bridge resistor

9, 10, ll, 12 is equal to R with, for example, R=lkfl and the amplifier 15 has a very high input resistance and a high amplification factor, for example, u=l0,000 while the amplifier 15 is adjusted in such a manner that in the absence of signals from the signal source I the potential of the input circuit and output circuit is equal to the fixed potential of the output terminal 2 of the signal source 1.

Dependent on the speech signal originating from the signal source 1 having a positive or negative polarity, the diode 6 will be conducting and the diode 5 will be blocked or conversely the diode 5 will be conducting and the diode 6 will be blocked, the amplifier 15 being negatively fed back either across the resistor II or across the resistor 12 through the then conducting diode. In case of an alternation of polarity a reversal of the negative feedback circuits of the amplifier 15 takes place, which negative feedback circuits are formed .by diode 6 and resistor 11 and diode 5 and resistor 12, respectively, and as a result of this reversal of the negative feedback circuits by means of polarity reversal a rectification of the signal originating from the signal source 1 takes place, which is diagrammatically shown in the Figure by the time diagram I8. The rectified signal from the signal source 1 occurs at the diagonal points l6, 17 of the bridge, in the embodiment shown, for example, the rectified signal is derived from diagonal point 17 for further handling in the user 7 by means of the amplifier 8 having the high input resistance.

Starting from the condition in which there is no signal from the signal source 1 available, the behavior of the polarity reversal arrangement in case of a positive and a negative signal voltage will be examined so as to explain the operation.

If, starting from this condition in which the diagonal point 13 and the input circuit and the output circuit of the amplifier 15 are thus connected to earth potential, at positive signal voltage from the signal source 1 is applied to the diagonal point 13 of the bridge, then a positive signal voltage will likewise occur at the input circuit of the amplifier l3 and a negative signal voltage will occur at the output of the amplifier 15, which already at an extremely small input signal opens the diode 6 due to the high amplification factor of the amplifier 15, so that the amplifier 15 will be negatively fed back through the resistor 11 and as a result of this negative feedback the amplifier 15 shows the tendency to counteract any variation in its input voltage, that is to say, the diagonal point 14 is substantially maintained at earth potential. When the signal voltage at the diagonal point 13 is 1 volt, a voltage of approximately 10 volts occurs, for example, at the diagonal point 14 connected to the input circuit of the amplifier 15.

The course of the current in the bridge in case of a positive signal voltage is shown for the purpose of illustration in the Figure by solid line arrows, during which no signal current is assumed by the

amplifiers

8 and 15 due to their high input resistances so that no distortions are caused thereby. If the diagonal point 13 connected to the signal source I has a positive signal voltage E, then a voltage of +(R/2R)E=-+-E/2 or (R/2AY)E='E/2 will occur at the

diagonal point

17, 16, respectively, under the circumstances mentioned at which the diagonal point 14 is substantially connected to earth potential and each

resistor

9, 10, l1, I2 is equal to R. When shown diagrammatically, voltages then occur at the diagonal points l7, 16 which voltages have a variation as is shown by the solid-line curves in the time diagrams 19, 20.

Conversely, the diode 5 will be opened when the signal voltage at the diagonal point 13 connected to the signal source I is negative and the amplifier 15 will be negatively fed back through the resistor 12, the diagonal point 14 connected to the input circuit of the amplifier 15 being maintained substantially at earth potential due to the negative feedback likewise as is the case for a positive signal voltage. The course of the current in the bridge is shown by the broken line arrows and voltages of -(R/2R)E -E/2 and +(R /2R)E=+E /2 will then occur at the

diagonal points

17, 16, respectively, when the signal voltage E at the diagonal point 13 connected to the signal source 1 is negative, while the variation of these voltages is shown by the broken line curves in the time diagrams I9, 20. As may be apparent from these time diagrams 19, 20, the rectified signals from the signal source 1 occur in a balanced form at the diagonal points l7, 16, the rectified signals at the diagonal point 17 in the embodiment shown being utilized for further handling in the user 7.

The polarity reversal in the circuit arrangement shown occurs exactly at the instant of the alternations of polarity of the signals to be transmitted so that due to the high amplification factor of the amplifier l5 and the negative feedback effect disturbing phenomena are prevented such as, for example, ageing phenomena, distortions in the amplifier l5 and the diodes S, 6, but also temperature effects and direct current drift phenomena since the negative feedback circuits of the amplifier also function as direct voltage negative feedback circuits.

If the signal source 1 is formed by a current source these direct current drift phenomena even exert no influence at all on the polarity reversal since due to the high internal resistance of the current source 1 the diagonal point 13 connected to the current source will assume the same potential as that of the diagonal point 14 connected to the input of the amplifier 15, so that consequently a voltage difference between these

diagonal points

13, 14 will not occur in the absence of a speech signal. If the signal source 1 is formed by a voltage source, the already slight influence of the direct current drift of the amplifier 15 can still further be reduced without disturbing the course of the current in the bridge by using an additional direct voltage negative feedback circuit in the amplifier 15 especially constructed for this purpose in the manner as is shown in the Figure.

Particularly, the amplifier 15 is provided with an input amplifier stage 21 employing a field effect transistor (FET), the source electrode being connected to the input of the subsequent amplifier stage 22 whilst the FET 21 which, as is known, has a very high input impedance is fed by a current source incorporated in the source electrode circuit in the form of a difference amplifier 23 provided with

transistors

24, 25 having a common emitter resistor 26. To compensate for the direct current drift of the amplifier, the base electrode of the transistor 24 is connected to earth potential through resistor 27, and the base electrode of the transistor 25 is connected to the output circuit of the amplifier 15 through a low-pass filter which does not pass signal frequencies and is composed of

series resistors

28, 29 and

shunt capacitors

30, 31.

In this case the direct current drift of the amplifier 15 is compensated for in the manner of a direct voltage negative feedback. If a direct current drift occurs, for example, at the output of the amplifier 15, the collector current of the transistor 24 and hence the current through the FET 21 will consequently start to vary low-pass filter 28-31 and the transistor 25 as a result of which also the voltage between the control electrode and the source electrode of the FET 21 will vary which voltage variation will bring about the direct current drift compensation of the amplifier 15 without a direct current being introduced into the control electrode circuit, or in other words, without the course of the current in the bridge 9-12 being disturbed.

The following data are mentioned below for a polarity reversal arrangement which was extensively tested in practice.

l3.9,l0,ll,l2: lKQ diodes 5, 6.- BAX l3. Resistors 28, 29: 5 KO Capacitors 30. 31: 10 pl.

Deviation in the polarity reversal arrangement: 0.! mv.

distortion level: smaller than 60 db. Transistors 24. 25: BCY H7.

Resistor 26: 3 K1] Resistor 27: [0 K0 FET 21; BFW I I.

In addition to the advantages of optimum results and simplicity in construction, the polarity reversal arrangement provides the great advantage of a great frequency independence, particularly the polarity reversal arrangement shown can be used for the lowest signal frequencies as occur, for example, in video signals.

In addition, the arrangement described is distinguished by its wide possibilities of use. The rectified output signals may be derived, for example, both in a balanced form and in single phase, and the possibility of capacitive coupling of the signal source 1 and the output amplifier 8 is provided without having to use extreme capacitances due to the possibility of using a. signal source 1 having a high internal resistance and an output amplifier 8 having a high input resistance.

If desired, there is the possibility of a transformer coupling of the signal source 1 to the bridge in which case the transformer is preferably incorporated between the

diagonal points

13, 14.

In the circuit arrangement described so far the polarity reversal takes place by the signals from the signal source 1 itself while using switching elements in the form of diodes 5, 6, whereas the polarity reversal in the circuit arrangement of FIG. 2 is effected by separate control signals, for example, for use of a circuit arrangement for pulse code demodulation shown in FIG. 2. The circuit arrangement of FIG. 2 is adapted for demodulation of pulse groups transmitted with the aid of pulse code modulation, wherein the first pulse wave always functions as a polarity pulse and the other pulses in a pulse group characterize the amplitude value of the rectified speech signal. Elements corresponding to those in FlG. 1 have the same reference numerals in FIG. 2.

ln the circuit arrangement for pulse code demodulation shown in FlG. 2 the pulse groups received through line 32 are applied to a pulse code demodulator 35 after suppressing the polarity pulse in an inhibitor gate 34; samplings occurring at the output circuit of the pulse code demodulator 35 which samplings have the variation shown in the time diagram 37 upon transmission of, for example, the signal as is illustrated in the time diagram 19 of FIG, 1. Both the inhibitor gate 34 and the pulse code demodulator 35 are controlled by a local pulse generator 33 which is accurately synchronized at the frequency of the received pulse groups, for example, by means of cotransmitted synchronizing pulses.

An AND-gate 38 controlled by the local pulse generator 33 is also connected to the line 32 for selection of the polarity pulses in the pulse groups, which selection gate 38 is succeeded by an inverter 39 connected to the local pulse generator 33 and has two

output lines

40, 41 for the control of a bistable trigger 42 which is likewise provided with two

control lines

43, 44 for the

electronic switching elements

45, 46 of the polarity reversal arrangement, each

electronic switching element

45, 46 being provided with a control electrode and, for example, formed by field effect transistors. in the arrangement shown the polarity pulses selected in the AND-gate 38 and consisting of l pulses at a position polarity and 0 pulses at a negative polarity are applied to the inverter 39 which applies a pulse to output line 40 in case of a 1 pulse as a polarity pulse and which applies a pulse to output line 41 in case of a 0 pulse as a polarity pulse, the bistable trigger 42 assuming one stable state as a result of the pulses of the output line 40 and assuming the other stable state as a result of the pulses of the output line 41. The control signals for the

electronic switching elements

45, 46 are derived in this manner from the

output circuits

43, 44 of the bistable trigger 42, which switching elements are consequently brought, for example, from their blocked condition to the conducting condition.

In fact, dependent on the polarity pulse being formed by a 1 pulse of a 0 pulse, the bistable trigger 42 supplies either a control signal for the electronic switching element 46 through control line 43, or a control signal for the electronic switching element 45 through control line 44, the polarity reversal being effected in the manner as already described with reference to FIG. 1 due to the mentioned control of the

electronic switching elements

45, 46. If, for example, a 1 pulse occurs as a polarity pulse indicating a signal of positive polarity to be transmitted, then the electronic switching element 46 is conducting and the sampling, which is then present at the output of the pulse code demodulator 35, occurs with positive polarity at the diagonal point 17 and with negative polarity at the diagonal point 16, whereas conversely for a 0 pulse as a polarity pulse indicating a signal of negative polarity to be transmitted, the electronic switching element 45 is conducting so that the sampling, which is then present at the output of the pulse code demodulator 35, occurs with negative polarity at the diagonal point 17 and with positive polarity at the output of the diagonal point 16. In this manner the samplings of the rectified signal at the diagonal point 13 shown in the time diagram 37 are converted by the polarity reversal arrangement into the samplings of the original signal which samplings are shown for the purpose of illustration in time diagrams 47, 48.

As may be evident from these time diagrams 47, 48, the samplings of the original signal occur in a balanced form at the diagonal points l6, 17 of the bridge, the diagonal point 17 likewise as in FIG. 1 being connected through an amplifier 49 having a high input resistance to a user 50, for example, a time multiplex distributor,

Finally it is to be noted that it is not necessary to make all resistor 9-12 of the bridge mutually equal, but that it is already sufficient to make the

resistors

9, 10 connected to the signal source 1 and the resistors ll, 12 connected to the input of the amplifier l5 pairwise equal.

What is claimed is I. A circuit arrangement for polarity reversal of signals from a signal source, which circuit arrangement is provided with two series-arranged electronic switching elements, characterized in that the polarity reversal arrangement is provided with a bridge composed of resistors, the signal source being connected to one end of a diagonal branch of the bridge and the input circuit of an amplifier which reverses the polarity of the input signal being connected to the other end of the said diagonal branch. the series arrangement of the two electronic switching elements being included between the ends of the other diagonal branch, the junction of the electronic switching elements being connected to the output circuit of the amplifier while the output signals of the polarity reversal arrangement are derived from one end of the last-mentioned diagonal branch of the bridge.

2. A circuit arrangement as claimed in claim 1, characterized in that output terminals of the signal source are connected to the said end of the diagonal branch and a point of fixed potential, respectively, while in the absence of signals from the signal source both the input circuit and the output circuit of the amplifier are adjusted to the said fixed potential.

3. A circuit arrangement as claimed in claim 1 wherein the bridge the two resistors connected to the signal source and the two resistors connected to the input of the amplifier have been made pairwise equal.

4. A circuit arrangement as claimed in claim I, wherein the amplifier is provided with an input amplifier stage employing a field effect transistor, the control electrode of said input amplifier stage being connected to the said end of the diagonal branch of the bridge and the source electrode being connected to a succeeding amplifier stage, while the input amplifier stage is fed by a current source in the form of a difference amplifier employing two transistors, the base electrode of one transistor being connected to a point of fixed potential and the base electrode of the other transistor being connected to the output of the amplifier through a low-pass filter which does not pass signal frequencies. g

5. A circuit arrangement as clalmed "'1 claim I, wherein the signal source is formed by a current source.

6. A circuit arrangement as claimed in claim 2, wherein the electronic switching elements are formed by diodes which, dependent on the polarity of the signals from the signal source, are brought from their blocked condition to the conducting condition.

7. A circuit arrangement as claimed in claim 1, wherein each electronic switching element is provided with a control electrode which are brought to their conducting condition by control signals through control lines connected to the control electrodes.

Claims

1. A circuit arrangement for polarity reversal of signals from a signal source, which circuit arrangement is provided with two series-arranged electronic switching elements, characterized in that the polarity reversal arrangement is provided with a bridge composed of resistors, the signal source being connected to one end of a diagonal branch of the bridge and the input circuit of an amplifier which reverses the polarity of the input signal being connected to the other end of the said diagonal branch, the series arrangement of the two electronic switching elements being included between the ends of the other diagonal branch, the junction of the electronic switching elements being connected to the output circuit of the amplifier while the output signals of the polarity reversal arrangement are derived from one end of the last-mentioned diagonal branch of the bridge.

3. A circuit arrangement as claimed in claim 1, wherein the bridge the two resistors connected to the signal source and the two resistors connected to the input of the amplifier have been made pairwise equal.

4. A circuit arrangement as claimed in claim 1, wherein the amplifier is provided with an input amplifier stage employing a field effect transistor, the control electrode of said input amplifier stage being connected to the said end of the diagonal branch of the bridge and the source electrode being connected to a succeeding amplifier stage, while the input amplifier stage is fed by a current source in the form of a difference amplifier employing two transistors, the base electrode of one transistor being connected to a point of fixed potential and the base electrode of the other transistor being connected to the output of the amplifier through a lowpass filter which does not pass signal frequencies.

5. A circuit arrangement as claimed in claim 1, wherein the signal source is formed by a current source.