WO2024200294A1

WO2024200294A1 - Current amplifier having a variable gain

Info

Publication number: WO2024200294A1
Application number: PCT/EP2024/057835
Authority: WO
Inventors: Carlo Fiocchi
Original assignee: Ams Italy SRL
Current assignee: Ams Italy SRL
Priority date: 2023-03-30
Filing date: 2024-03-22
Publication date: 2024-10-03
Anticipated expiration: 2025-09-30

Abstract

A current amplifier (10) comprises an amplifying current mirror (110) having a variable gain k, the amplifying current mirror (110) comprising an input branch (114) and a variable output branch (115). The current amplifier (10) further comprises a first current source (105) for providing a reference current to the output branch (115). Moreover, the current amplifier (10) comprises a biasing circuit (120) configured to generate a variable current, which is based on the reference current and the variable gain k, and to deliver the variable current to the input branch (114) of the amplifying current mirror (110). The biasing circuit (120) comprises a biasing current mirror (130) having a gain that is adjustable on the basis of the variable gain k.

Description

CURRENT AMPLIFIER HAVING A VARIABLE GAIN

The present disclosure refers to a current amplifier having a variable gain.

Current amplifiers in which the gain can be adjusted in integer steps are applied in a variety of applications. For example, a current mirror may be used for amplifying a signal current. Generally, attempts are being made to improve a variable current amplifier.

It is an object of the present invention to provide an improved current amplifier.

SUMMARY

According to embodiments, the above object is achieved by the claimed matter according to the independent claims.

According to embodiments, a current amplifier comprises an amplifying current mirror having a variable gain k, the amplifying current mirror comprising an input branch and a variable output branch. The current amplifier further comprises a first current source for providing a reference current to the output branch. Moreover, the current amplifier comprises a biasing circuit configured to generate a variable current, which depends from the reference current and the variable gain k, and to deliver the variable current to the input branch of the amplifying current mirror. The biasing circuit comprises a biasing current mirror having a gain that is adjustable on the basis of the variable gain k. For example , the biasing current mirror may form part of a feedback circuit configured to generate the variable current .

According to embodiments , the biasing current mirror may comprise a generator branch and a variable branch having the variable gain .

By way of example , the biasing circuit further comprises a second current source providing a current that depends from the reference current , the second current source being connected to the variable branch .

According to embodiments , the feedback circuit comprises a relay device having an input and an output , and the generator branch of the biasing current mirror comprises a diode- connected transistor . A terminal of the diode-connected transistor is coupled to the output of the relay device , and the input of the relay device is coupled to the second current source .

For example , the relay device may comprise a level-shi fting transistor . A terminal of the diode-connected transistor may be connected to a source terminal of the level shi fting transistor, and a gate of the level-shi fting transistor may be coupled to the variable branch .

According to embodiments , the variable output branch of the ampli fying current mirror comprises a plurality of devices and corresponding switches that are configured to be activated by a digital command .

Further, the variable branch of the biasing current mirror may comprise a plurality of devices and corresponding switches that are configured to be activated by the digital command . BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles. Other embodiments of the invention and many of the intended advantages will be readily appreciated, as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numbers designate corresponding similar parts.

Fig. 1A is an equivalent circuit diagram of a current amplifier according to embodiments.

Fig. IB is an equivalent circuit diagram of a current amplifier according to further embodiments.

Fig. 2 shows an equivalent circuit diagram of a current amplifier according to further embodiments.

DETAILED DESCRIPTION

In the following detailed description reference is made to the accompanying drawings, which form a part hereof and in which are illustrated by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology such as "top", "bottom", "front", "back", "over", "on", "above", "leading", "trailing" etc. is used with reference to the orientation of the Figures being described. Since components of embodiments of the invention can be positioned in a number of di f ferent orientations , the directional terminology is used for purposes of illustration and is in no way limiting . It is to be understood that other embodiments may be utili zed and structural or logical changes may be made without departing from the scope defined by the claims .

The description of the embodiments is not limiting . In particular, elements of the embodiments described hereinafter may be combined with elements of di f ferent embodiments .

As employed in thi s speci fication, the terms "coupled" and/or "electrically coupled" are not meant to mean that the elements must be directly coupled together - intervening elements may be provided between the "coupled" or "electrically coupled" elements . The term "electrically connected" may describe a low-ohmic electric connection between the elements electrically connected together .

According to further embodiments and where appropriate , the term "electrically connected" may mean that the respective elements are "directly connected" or are "directly and permanently connected" .

As used herein, the terms "having" , "containing" , " including" , "comprising" and the like are open ended terms that indicate the presence of stated elements or features , but do not preclude additional elements or features . The articles "a" , "an" and "the" are intended to include the plural as well as the singular, unless the context clearly indicates otherwise .

Within the present disclosure , elements of an electrical circuit are described by referring to speci fic types of transistors , e . g . PMOS and NMOS transistors . As is to be clearly understood, the corresponding disclosure is not limiting . In particular, PMOS transistors may be replaced by NMOS transistor and vice versa while adapting the further circuitry where appropriate , as is generally known to the person skilled in the art . Further, where appropriate , illustrated NMOS and PMOS transistors may be replaced by further transistor types , e . g . bipolar transistors .

Fig . 1A shows an equivalent circuit diagram of a current ampli fier 10 according to embodiments . As will be explained in the following, the current ampli fier 10 comprises an ampli fying current mirror 110 having a variable gain k . The ampli fying current mirror 110 comprises an input branch 114 and a variable output branch 115 . For example , the variable input branch 114 may comprise a diode-connected transistor 111 . Moreover, the variable output branch 115 may comprise a variable transistor 112 . For example , by adj usting the ratio between the variable transistor 112 and the diode-connected transistor 111 , a gain k may be set . The current ampli fier 10 further comprises a first current source for providing a reference current Io to the output branch . Moreover, the current ampli fier 10 comprises a biasing circuit 120 which is configured to generate a variable current which depends from the reference current Io and the variable gain k . The biasing circuit 120 is configured to deliver the variable current to the input branch 114 of the ampli fying current mirror 110 . The biasing circuit 120 comprises a biasing current mirror 130 which has a gain that is adj ustable on the basis of the variable gain k .

As is illustrated in Fig . 1A, for example , an input current In may be fed to the input branch 114 of the ampli fying current mirror 110 . An output current lout is output from the variable output branch 115 . In an ampli fying current mirror 110 as illustrated in Fig . 1A, a bias current is superimposed to the input signal In in order to keep constant the sign of the overall current . As a result , signal recti fication is avoided . In order to avoid a net output current that is caused by the reference current , the ratio between the bias currents supplied to the input branch 114 and supplied to the output branch 115 should be equal to the mirror gain k . As is illustrated in Fig . 1A, a first current source 105 is configured to supply a reference current Io to the output branch 115 . For example , the reference current Io may be constant . The first current source 105 may be connected to a supply voltage , e . g . V_DD . Further, the current input to the input branch 114 is varied according to the gain k .

The variable current Ii input to the input branch 114 is generated using the biasing circuit 120 . The biasing circuit 120 comprises a biasing current mirror 130 which has a gain that is adj ustable on the basis of the variable gain k . The biasing current mirror 130 may form part of a feedback circuit 127 which is configured to generate the variable current Ii . For example , the variable current Ii may be sensed and mirrored to bias the input branch 114 of the current ampli fier 100 according to generally known methods . According to implementations , the biasing circuit 120 may be connected to the ampli fying circuit 100 using a further current mirror . Accordingly, a current supplied to the input branch 114 may be equal to or depend on the current supplied by the biasing circuit 120 .

As is shown in the left-hand part of Fig . 1A, the biasing circuit 120 may comprise a second current source 125 which may e . g . generate the reference current Io or any other suitable constant current that is related to the reference current Io generated by the first current source 105 . For example , the feedback circuit 127 may be configured to generate the variable current that is based on the reference current Io and the gain k .

According to the configuration of Fig . 1A, the feedback circuit 127 comprises a biasing current mirror 130 . The biasing current mirror 130 may comprise a variable branch 137 comprising a variable transistor 132 . The biasing current mirror 130 may further comprise a generator branch 136 comprising a diode-connected transistor 131 . A terminal of the variable transistor 132 is connected to the second current source 125 via a node 126 . The feedback circuit 127 may comprise a relay device 138 having an input 139 and an output 140 . The input 139 of the relay device 138 is coupled to the node 126 . The output of the relay device 138 is coupled to the generator branch 136 . In more detail , the output of the relay device 138 may source the current to the diode-connected transistor 131 of the biasing current mirror 130 . This implements a feedback loop . As a result the currents provided by the second current source 125 and by the variable transistor 132 must match, and the current Ii in the diode- connected transistor 131 may be equal to lo/ k . For example , the relay device 138 may be implemented by an ampli fier . For example , the second current source 125 may be connected to the supply voltage .

According to embodiments illustrated in Fig . IB, the relay device 138 may comprise a level-shi fting transistor 133 . The node 126 may be connected to the gate electrode of a levelshi fting transistor 133 . A source terminal of the levelshi fting transistor 133 may be coupled to a terminal of the diode-connected transistor 131 . As is illustrated, according to embodiments, the output current is kept constant, independent from the gain set by the current mirror. Consequently, the input current is changed in dependence of the gain.

According to embodiments illustrated in Fig. IB, the biasing circuit 120 may be connected to the amplifying circuit 100 using a further current mirror 117. A drain terminal of the level-shifting transistor 133 may be coupled to the third current mirror 117, e.g. the diode-connected transistor of the third current mirror 117. The source terminals of the transistor implementing the third current mirror 117 may be connected to the supply voltage, e.g. V_DD. Further elements of the amplifier 10 illustrated in Fig. IB are similar or identical with corresponding elements of the amplifier illustrated in Fig. 1A.

In the feedback circuit 127, a current value, e.g. Io is forced to the drain terminal of the variable transistor 132. Further, the diode-connected transistor 131 receives its current from the level-shifting transistor 133. The circuit arrangement of the level-shifting transistor 133 and the diode-connected transistor 131 implements a source follower amplifying circuit. As a consequence, the level-shifting transistor 133 may be configured to set a current that is precisely equal or scaled to lo/k due to the presence of the closed feedback loop implemented by the feedback circuit 127. The current mirror 117 is configured to mirror the current generated by the biasing circuit 120 to the input branch 114 of the amplifying circuit 100.

Hence, according to embodiments illustrated in Figs. 1A and

IB, the current amplifying circuit 100 is properly biased. Fig. 2 shows an implementation of the current amplifier 10 illustrated in Figs. 1A and IB. As is shown, the variable transistor 112 of the variable output branch 115 of the amplifying current mirror 110 may comprise a plurality of devices, e.g. transistor elements 116i that may be connected in parallel to each other by means of switches 113i. For example, the single transistor elements 116i may be activated using a digital command (bo, bi, ... b_n) .

Moreover, the variable transistor 132 of the biasing current mirror 130 may comprise a plurality of devices, e.g. transistor elements 135i that may be connected in parallel using switches 134i. For example, the switches 134i may be activated using a digital command (bo, bi, ... b_n) . For example, the digital command for activating the variable transistor 132 may be identical to or derived from a digital command for setting the variable output branch 115 of the amplifying circuit 100.

As a result, using one digital command, the variable gain k of the current amplifier may be set. At the same time, the bias current may be scaled to provide a bias current corresponding to the reference current divided by the gain ratio k.

As a result, the bias current is reduced, while the current in the output branch is kept constant. As a consequence, the power consumption is kept constant regardless the value of the gain. Hence, an increase of the reference current due to a varying gain may be avoided which is desirable for many applications, in which a load has to be protected from excessive currents, e.g. LED current generators. Further, as has been shown, the gain may be adjusted in integer steps over a large range without constraints. While embodiments of the invention have been described above , it is obvious that further embodiments may be implemented . For example , further embodiments may comprise any subcombination of features recited in the claims or any subcombination of elements described in the examples given above . Accordingly, this spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein .

LIST OF REFERENCES

10 current ampli fier

100 ampli fying circuit

105 first current source

110 ampli fying current mirror

111 diode-connected transistor

112 variable transistor

1131 switch

114 input branch

115 variable output branch

1161 transistor element

117 third current mirror

120 biasing circuit

125 second current source

126 node

127 feedback circuit

130 biasing current mirror

131 diode-connected transistor

132 variable transistor

133 level-shi fting transistor

1341 switch

1351 transistor element

136 generator branch

137 variable branch

138 relay device

139 input of relay device

140 output of relay device

Claims

1. A current amplifier (10) comprising: an amplifying current mirror (110) having a variable gain k, the amplifying current mirror (110) comprising an input branch (114) and a variable output branch (115) , the current amplifier (10) further comprising a first current source (105) for providing a reference current to the output branch (115) , and a biasing circuit (120) configured to generate a variable current, which depends from the reference current and the variable gain k, and to deliver the variable current to the input branch (114) of the amplifying current mirror (110) , the biasing circuit (120) comprising a biasing current mirror (130) having a gain that is adjustable on the basis of the variable gain k.

2. The current amplifier (10) according to claim 1, wherein the biasing current mirror (130) forms part of a feedback circuit (127) configured to generate the variable current .

3. The current amplifier (10) according to claim 2, wherein the biasing current mirror (130) comprises a generator branch (136) and a variable branch (137) having the variable gain .

4. The current amplifier (10) according to claim 3, wherein the biasing circuit (120) further comprises a second current source (125) providing a current that depends from the reference current, the second current source (125) being connected to the variable branch (137) .

5. The current amplifier (10) according to claim 4, wherein the feedback circuit (127) comprises a relay device (138) having an input (139) and an output (140) , and the generator branch (136) of the biasing current mirror (130) comprises a diode-connected transistor (131) , a terminal of the diode-connected transistor (131) being coupled to the output (140) of the relay device (138) , the input (139) of the relay device (138) being coupled to the second current source (125) .

6. The current amplifier (10) according to claim 5, wherein the relay device (138) comprises a level-shifting transistor (133) , a terminal of the diode-connected transistor (131) being connected to a source terminal of the level shifting transistor (133) , and a gate of the level-shifting transistor (133) being coupled to the second current source (125) to the variable branch (137) .

7. The current amplifier (10) according to any of the preceding claims, wherein the variable output branch (115) of the amplifying current mirror (110) comprises a plurality of devices (116i) and corresponding switches (113i) that are configured to be activated by a digital command.

8. The current amplifier (10) according to claim 7, wherein the variable branch (137) of the biasing current mirror comprises a plurality of devices (135i) and corresponding switches (134i) that are configured to be activated by the digital command.