EP3671775A1 - Integrated circuit comprising a balun - Google Patents
Integrated circuit comprising a balun Download PDFInfo
- Publication number
- EP3671775A1 EP3671775A1 EP18212964.3A EP18212964A EP3671775A1 EP 3671775 A1 EP3671775 A1 EP 3671775A1 EP 18212964 A EP18212964 A EP 18212964A EP 3671775 A1 EP3671775 A1 EP 3671775A1
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- EP
- European Patent Office
- Prior art keywords
- balun
- inductor coil
- integrated circuit
- coupled
- capacitance
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F21/00—Variable inductances or transformers of the signal type
- H01F21/12—Variable inductances or transformers of the signal type discontinuously variable, e.g. tapped
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/28—Coils; Windings; Conductive connections
- H01F27/2804—Printed windings
Definitions
- the present specification relates to an integrated circuit comprising a semiconductor substrate and a balun.
- the present specification also relates to method of making such an integrated circuit.
- balun balanced to unbalanced converter
- a monolithically integrated balun is usually implemented with symmetrically coupled inductors.
- the parasitic capacitive coupling can cause an imbalance, resulting in a finite common-mode rejection ratio (CMRR). Imperfect balance could give rise to undesired common-mode signal injection (noise, etc.) and common- or mixed-mode instability.
- CMRR common-mode rejection ratio
- an integrated circuit comprising:
- a method of making an integrated circuit comprising:
- CMRR common mode rejection ratio
- the capacitance (coupled to the center tap) for tuning a common mode rejection ratio of the balun may comprise a capacitor component having first and second capacitor plates.
- the capacitance (coupled to the center tap) for tuning a common mode rejection ratio of the balun may comprise a ground shield located on or in the semiconductor substrate.
- the use of a ground shield in this way can simultaneously provide shielding for the balun and tuning of the CMRR by configuring (e.g. the shape and size of) the ground shield to select the capacitance that it provides.
- the capacitance (coupled to the center tap) for tuning a common mode rejection ratio of the balun may comprise a combination of a ground shield and a separate capacitor component having first and second capacitor plates as noted above.
- the ground shield may be located adjacent (e.g. underneath) the primary and secondary inductor coils.
- the ground shield may be coupled to the center tap of the secondary inductor coil. This can provide optimal tuning of the CMRR.
- the first end of the primary inductor coil may be coupled to said reference voltage via a capacitance for tuning a common mode rejection ratio of the balun. This can allow for further tuning of the CMRR by choosing the value of the capacitance.
- the primary inductor coil and the secondary inductor coil may comprise patterned metal features located in a metallization stack on a major surface of the semiconductor substrate.
- the ground shield may comprise a patterned metal feature located in a metal layer of the metallization stack.
- the center tap may form a virtual ground node of the secondary inductor coil.
- the reference voltage to which the center tap of the secondary inductor coil may be coupled via said capacitance may be ground.
- the reference voltage to which the first end of the primary inductor coil is coupled may be ground.
- a differential transceiver comprising the integrated circuit of any of claims 1 to 11.
- a power amplifier comprising the integrated circuit of any of claims 1 to 11.
- a low noise amplifier comprising the integrated circuit of any of claims 1 to 11.
- FIG. 1 shows a balun 10 according to an embodiment of this disclosure.
- the balun 10 is provided on an integrated circuit.
- the integrated circuit comprises a semiconductor substrate, which may for instance comprise silicon. Further details of the construction and manufacture of a balun 10 of the kind disclosed herein will be set out below in relation to Figures 3 to 6 .
- the balun 10 in Figure 1 includes a primary inductor coil 14 and a secondary inductor coil 12.
- the primary inductor coil 14 has a first end and a second end, with a number of windings located in-between.
- the first end of the primary inductor coil 14 is coupled to a reference voltage 20.
- the reference voltage 20 may be ground.
- the second end of the primary inductor coil 14 forms a single ended input 6 of the balun.
- the secondary inductor coil 12 has a first end and a second end, which form a differential output 2, 4 of the balun 10.
- the capacitance between the ends of the primary inductor coil 14 and the secondary inductor coil 12 are represented in Figure 1 by the capacitances 16, 18.
- the secondary inductor coil 12 is provided with a center tap 11.
- the center tap 11 is typically provided at a point located midway along the turn(s) between the first end and the second end of the secondary inductor coil 12.
- the center tap 11 may thus form a virtual ground node of the secondary inductor coil 12.
- the center tap 11 is coupled to a reference voltage 30.
- the reference voltage 30 may be ground.
- the center tap 11 is coupled to the reference voltage 30 via a capacitance 40.
- the coupling of a center tap 11 of the secondary inductor coil 12 to a reference voltage via the capacitance 40 in this way can allow a common mode rejection ratio (CMRR) of the balun 10 to be tuned. This may be achieved by, for instance, selecting the value of the capacitance. Accordingly, the performance of the device may be improved.
- CMRR common mode rejection ratio
- the capacitance 40 may be implemented as a separate capacitor component having first and second capacitor plates, coupled between the center tap 11 and the reference voltage 30.
- tuning the CMRR may be achieved conveniently by choosing the capacitance value of the separate capacitor component.
- the capacitance 40 may be implemented using a ground shield of the balun 10.
- the ground shield is typically located on or in the semiconductor substrate (e.g. adjacent to (e.g. beneath) the primary inductor coil 14 and the secondary inductor coil 12).
- the ground shield in such embodiments is connected to the virtual ground node provided by the center tap 11.
- the use of a ground shield in this way can simultaneously provide electromagnetic (EM) shielding for the balun 10 and tuning of the CMRR by configuring (e.g. the shape and size of) the ground shield to select the capacitance that it provides.
- EM electromagnetic
- the capacitance 40 may be implemented using a combination of a ground shield and a separate capacitor component as noted above.
- FIG. 2 shows a balun 10 according to another embodiment of this disclosure.
- the balun 10 in Figure 2 is similar to the balun 10 shown in Figure 1 , and only the differences will be described below.
- the balun 10 in Figure 2 is provided with a capacitance 42.
- the first end of the primary inductor coil 14 is coupled to the reference voltage 20 via the capacitance 42.
- the capacitance 42 may be implemented as a separate capacitor component having first and second capacitor plates, coupled between the first end of the primary inductor coil 14 and the reference voltage 20.
- further tuning of the CMRR may be achieved conveniently by choosing the capacitance value of the separate capacitor component.
- the CMRR tuning in the embodiment of Figure 2 may thus be provided by a combination of the capacitance 40 and the capacitance 42.
- the capacitance 40 may be implemented as a separate capacitor component and/or by a ground shield.
- Figures 3-5 show the various metal layers of a balun 10 according to an embodiment of this disclosure.
- the primary inductor coil 14 and the secondary inductor coil 12 described above may be implemented as patterned metal features located in a metallization stack 100 on a major surface of the semiconductor substrate of the integrated circuit.
- metallization stacks typically include a plurality of metal layers including lithographically patterned metal features.
- the stack 100 typically also includes via layers, which are sandwiched between the metal layers.
- the via layers include electrically conductive vias, for interconnecting the patterned metal features located in the neighbouring metal layers.
- the metallization stack 100 includes at least six metal layers (M1, M2, M3, M4, M5, M6) and intervening via layers (VI, V2, V3, V4, V5).
- the primary inductor coil 14 and the secondary inductor coil 12 are implemented in metal layers M4, M5 and M6.
- Figure 3 shows the patterned metal features located in metal layer M4, plus the features located in the via layer (V4) between M4 and M5.
- Figure 4 shows the patterned metal features located in metal layer M5, plus the features located in the via layer (V5) between M5 and M6.
- Figure 5 shows the patterned metal features located in metal layer M6, plus (again) the features located in the via layer (V5) between M5 and M6.
- the metal feature 52 forms the part of the secondary inductor coil 12 located in M4 and V4.
- the metal features 54 form the differential output of the balun.
- the metal features 56 is located in via layer V4 and connect the features 54 to corresponding features in metal layer M5.
- metal feature 62 forms the part of the secondary inductor coil 12 located in M5.
- Metal feature 64 forms the part of the primary inductor coil 14 located in M5.
- Metal feature 69A forms a first end of the primary inductor coil 14, which may be coupled to a reference voltage.
- Metal feature 69B forms a second end of the primary inductor coil 14, which forms the single ended input of the balun.
- Metal features 67 which are located in via layer V5, connect the features of the primary inductor coil 14 in M5 to the features of the primary inductor coil 14 in M6.
- Metal features 66 which are located in via layer V5, connect the features of the secondary inductor coil 12 in M5 to the features in metal layer M6.
- Metal features 68 form the differential output of the balun (along with the features 54 shown in Figure 3 ).
- the metal feature 70 forms the part of the secondary inductor coil 12 located in M6.
- the metal feature 72 forms the part of the primary inductor coil 14 located in M6.
- Metal features 66 located in via layer V5 are also visible in Figure 5 .
- Metal feature 74 forms a ground reference ring around the structure, which have the purpose of defining the input and output common-mode ground potential both at the primary and secondary inductor coil positions.
- Figure 6 shows, in addition to the features of Figure 5 , the optional provision of a patterned ground shield formed by metal feature 110.
- the metal feature 110 forming the ground shield may be provided adjacent the primary inductor coil 14 and the secondary inductor coil 12. For instance, as shown in Figure 6 , the metal feature 110 forming the ground shield is provided beneath the primary inductor coil 14 and the secondary inductor coil 12.
- the capacitance 40 of the balun 10 may be implemented at least in part by a ground shield.
- Figure 6 shows some of the metal layers of a balun according to another embodiment of this disclosure, in which such a ground shield 110 is included. Note that the features of the primary inductor coil 14, the secondary inductor coil 12, the center tap 11 and so on in this embodiment may be substantially as already described above in relation to Figure 3 to 5 .
- the ground shield 110 may be provided in a metal layer of a via layer of the metallization stack 100.
- the ground shield in this embodiment is located beneath the primary 14 and secondary 12 inductor coils.
- the turns of the primary 14 and secondary 12 inductor coils may be located within an outer peripheral edge of the ground shield 110.
- a method of making integrated circuit may include the following steps.
- the method includes providing a semiconductor substrate.
- the substrate may, for instance, be a silicon substrate. It is envisaged that the substrate may comprise part of a larger wafer, which may subsequently be singulated (diced), for manufacturing a plurality of like integrated circuits, each including a balun according to the present disclosure.
- the substrate may, as part of the back end of line (BEOL) manufacturing process, be provided with a metallization stack 100.
- the stack 100 may include features for interconnecting components of the integrated circuit located in the substrate and for providing input/output terminals to the substrate.
- the metallization stack 100 may also include patterned metal features implementing the balun 10.
- the method may also include forming a balun on a major surface of the substrate. This may be done by using BEOL metallization techniques to form the primary inductor coil 14 and the secondary inductor coil 12, the center tap 11 and optional ground shield 110.
- the primary inductor coil 14 has a first end and a second end. The first end of the primary inductor coil 14 is coupled to a reference voltage, which may be ground. For instance, the first end of the primary inductor coil 14 may be coupled to a ground terminal of the substrate. The second end of the primary inductor coil 14 forms a single ended input of the balun.
- the secondary inductor coil 12 has a first end and a second end, which form the differential output of the balun 10.
- the secondary inductor coil also has a center tap 11 coupled to a reference voltage via a capacitance for tuning a common mode rejection ratio of the balun 10.
- the reference voltage may be ground (e.g. the capacitance may be coupled to a ground terminal of the substrate).
- capacitances 40 and 42 comprise separate capacitor components, these may also be implemented in the metallization stack, for instance by providing patterned metal features forming the capacitor plates thereof.
- Figure 7 shows a balun
- Figure 8 models the phase imbalance, amplitude imbalance and CMRR of the balun of Figure 7 .
- the second end of the primary inductor coil (i.e. the end that forms the single ended input) of the balun is labelled as terminal 1
- the first end of the secondary inductor coil of the balun is labelled as terminal 2
- the second end of the secondary inductor coil of the balun is labelled as terminal 3.
- the inductance of the primary inductor coil may be denoted as L p
- the inductance of the secondary inductor coil may be denoted as L s .
- L s includes two contributions L s/2 , each from a respective part of the secondary inductor coil that is located on either side of the center tap.
- the capacitance between the primary inductor coil and the secondary inductor coil of the balun is represented by the capacitances C p .
- the upper graph models the phase imbalance 80 and the amplitude imbalance 81 of the balun of Figure 7
- the lower graph models the CMRR 82.
- the balun of Figure 7 exhibits imperfect imbalance and limited CMRR.
- Figure 9-10 show a network analysis of a balun according to an embodiment of this disclosure.
- CMRR_Z Z 31 ⁇ Z 0 + Z 22 + Z 32 ⁇ Z 21 ⁇ Z 0 + Z 33 + Z 32 Z 31 ⁇ Z 0 + Z 22 ⁇ Z 32 + Z 21 ⁇ Z 0 + Z 33 ⁇ Z 32
- Z 32 Z 22 + Z 0 ⁇ CMRR_Z ⁇ Z 31 ⁇ Z 21 Z 31 + Z 21
- condition Z 31 + Z 21 may be satisfied.
- this goal may be reached by adding a compensation capacitor (CCM) for the common-mode signals (note that in Figure 10 the balun is modeled by two mutually coupled inductors L 1 and L 2 ).
- CCM compensation capacitor
- Z 21 v 2 i 1
- Z 31 v 3 i 1
- the upper graph models the phase imbalance 83 and the amplitude imbalance 84 of a balun of the kind shown in Figure 1 , which includes a center tap 11 provided at a point located midway along the turn(s) between the first end and the second end of the secondary inductor coil 12, and in which the center tap 11 is coupled to ground via a capacitance 40.
- the lower graph in Figure 11 models CMRR Z 85 and CMRR 86 of the balun 10.
- the capacitance 40 of the balun 10 modelled in Figure 11 comprises a separate capacitor component as noted above.
- a balun according to an embodiment of this invention has an improved balance and an improved CMRR (>34dB and the bandwidth of the device).
- a particular bandwidth of interest is in the range 26-30 GHz.
- the upper graph models the phase imbalance 87 and the amplitude imbalance 88 of a balun of the kind shown in Figure 2 , which includes a center tap 11 provided at a point located midway along the turn(s) between the first end and the second end of the secondary inductor coil 12, in which the center tap 11 is coupled to ground via a capacitance 40, and in which the first end of the primary inductor coil 14 is coupled to a reference voltage 20 via the capacitance 42.
- the lower graph in Figure 12 models CMRR_Z 89 and CMRR 90 of the balun 10.
- the capacitances 40 and 42 of the balun 10 modelled in Figure 12 each comprise a separate capacitor component as noted above.
- a balun according to an embodiment of this invention has a further improved balance and a further improved CMRR (>42dB and the bandwidth of the device).
- CMRR >42dB and the bandwidth of the device.
- a particular bandwidth of interest is in the range 26-30 GHz.
- the upper graph models the phase imbalance 91 and the amplitude imbalance 92 of a balun of the kind shown in Figure 1 , which includes a center tap 11 provided at a point located midway along the turn(s) between the first end and the second end of the secondary inductor coil 12, and in which the center tap 11 is coupled to ground via a capacitance 40.
- the lower graph in Figure 13 models CMRR_Z 93 and CMRR 94 of the balun 10.
- the capacitance 40 of the balun 10 modelled in Figure 13 comprises a combination of separate capacitor component and a ground shield 110 of the kind described above in relation to Figure 6 .
- a balun according to an embodiment of this invention has a yet further improved balance and a yet further improved CMRR (>40dB and the bandwidth of the device).
- CMRR >40dB and the bandwidth of the device.
- a particular bandwidth of interest is in the range 26-30 GHz.
- the upper graph models the phase imbalance 95 and the amplitude imbalance 96 of a balun of the kind shown in Figure 2 , which includes a center tap 11 provided at a point located midway along the turn(s) between the first end and the second end of the secondary inductor coil 12, in which the center tap 11 is coupled to ground via a capacitance 40, and in which the first end of the primary inductor coil 14 is coupled to a reference voltage 20 via the capacitance 42.
- the lower graph in Figure 14 models CMRR_Z 97 and CMRR 98 of the balun 10.
- the capacitance 40 of the balun 10 modelled in Figure 14 comprises a combination of separate capacitor component and a ground shield 110 of the kind described above in relation to Figure 6 .
- the capacitance 42 of the balun 10 modelled in Figure 14 comprises a separate capacitor component as noted above.
- a balun according to an embodiment of this invention also has a yet further improved balance and a yet further improved CMRR (>50dB and the bandwidth of the device). Again, in accordance with an embodiment of this disclosure, a particular bandwidth of interest is in the range 26-30 GHz.
- a differential transceiver (e.g. for operation at RF and mmWave frequencies) including an integrated circuit having a balun 10 of the kind described above.
- a differential transceiver may be provided in mobile or fixed network systems.
- a power amplifier (PA) including an integrated circuit having a balun 10 of the kind described above, in which the balun 10 operates as an output balun of the power amplifier.
- PA power amplifier
- LNA low noise amplifier
- the integrated circuit includes a semiconductor substrate.
- the integrated circuit also includes a balun.
- the balun includes a primary inductor coil having a first end and a second end. The first end of the primary inductor coil is coupled to a reference voltage. A second end of the primary inductor coil forms a single ended input of the balun.
- the balun also includes a secondary inductor coil having a first end and a second end. The first end and the second end form a differential output of the balun.
- the secondary inductor coil has a center tap coupled to a reference voltage via a capacitance for tuning a common mode rejection ratio of the balun.
Abstract
An integrated circuit and a method of making the same. The integrated circuit includes a semiconductor substrate. The integrated circuit also includes a balun. The balun includes a primary inductor coil having a first end and a second end. The first end of the primary inductor coil is coupled to a reference voltage. A second end of the primary inductor coil forms a single ended input of the balun. The balun also includes a secondary inductor coil having a first end and a second end. The first end and the second end form a differential output of the balun. The secondary inductor coil has a center tap coupled to a reference voltage via a capacitance for tuning a common mode rejection ratio of the balun.
Description
- The present specification relates to an integrated circuit comprising a semiconductor substrate and a balun. The present specification also relates to method of making such an integrated circuit.
- At RF and mmWave frequencies, a balun (balanced to unbalanced converter) is used to transform a single-ended signal to a differential signal. A monolithically integrated balun is usually implemented with symmetrically coupled inductors. At high frequencies the parasitic capacitive coupling can cause an imbalance, resulting in a finite common-mode rejection ratio (CMRR). Imperfect balance could give rise to undesired common-mode signal injection (noise, etc.) and common- or mixed-mode instability.
- Aspects of the present disclosure are set out in the accompanying independent and dependent claims. Combinations of features from the dependent claims may be combined with features of the independent claims as appropriate and not merely as explicitly set out in the claims.
- According to an aspect of the present disclosure, there is provided an integrated circuit comprising:
- a semiconductor substrate; and
- a balun comprising:
- a primary inductor coil having a first end and a second end, wherein the first end of the primary inductor coil is coupled to a reference voltage, and wherein the second end of the primary inductor coil forms a single ended input of the balun; and
- a secondary inductor coil having a first end and a second end, wherein the first end and the second end form a differential output of the balun, and wherein the secondary inductor coil has a center tap coupled to a reference voltage via a capacitance for tuning a common mode rejection ratio of the balun.
- According to another aspect of the present disclosure, there is provided a method of making an integrated circuit, the method comprising:
- providing a semiconductor substrate; and
- forming a balun on a major surface of the substrate by:
- forming a primary inductor coil having a first end and a second end, wherein the first end of the primary inductor coil is coupled to a reference voltage, and wherein the second end of the primary inductor coil forms a single ended input of the balun; and
- forming a secondary inductor coil having a first end and a second end, wherein the first end and the second end form a differential output of the balun, and wherein the secondary inductor coil has a center tap coupled to a reference voltage via a capacitance for tuning a common mode rejection ratio of the balun.
- The coupling of a center tap of the secondary inductor coil coupled to a reference voltage via a capacitance can allow a common mode rejection ratio (CMRR) of the balun to be tuned (e.g. by selecting the value of the capacitance). This may improve the performance of the device.
- Conveniently, the capacitance (coupled to the center tap) for tuning a common mode rejection ratio of the balun may comprise a capacitor component having first and second capacitor plates.
- The capacitance (coupled to the center tap) for tuning a common mode rejection ratio of the balun may comprise a ground shield located on or in the semiconductor substrate. The use of a ground shield in this way can simultaneously provide shielding for the balun and tuning of the CMRR by configuring (e.g. the shape and size of) the ground shield to select the capacitance that it provides. It is envisaged that the capacitance (coupled to the center tap) for tuning a common mode rejection ratio of the balun may comprise a combination of a ground shield and a separate capacitor component having first and second capacitor plates as noted above.
- For effective shielding of the inductor coils, the ground shield may be located adjacent (e.g. underneath) the primary and secondary inductor coils.
- The ground shield may be coupled to the center tap of the secondary inductor coil. This can provide optimal tuning of the CMRR.
- The first end of the primary inductor coil may be coupled to said reference voltage via a capacitance for tuning a common mode rejection ratio of the balun. This can allow for further tuning of the CMRR by choosing the value of the capacitance.
- Conveniently, the primary inductor coil and the secondary inductor coil may comprise patterned metal features located in a metallization stack on a major surface of the semiconductor substrate.
- Conveniently, the ground shield may comprise a patterned metal feature located in a metal layer of the metallization stack.
- The center tap may form a virtual ground node of the secondary inductor coil.
- The reference voltage to which the center tap of the secondary inductor coil may be coupled via said capacitance may be ground.
- The reference voltage to which the first end of the primary inductor coil is coupled may be ground.
- According to a further aspect of the present disclosure, there is provided a differential transceiver comprising the integrated circuit of any of
claims 1 to 11. - According to another aspect of the present disclosure, there is provided a power amplifier comprising the integrated circuit of any of
claims 1 to 11. - According to a further aspect of the present disclosure, there is provided a low noise amplifier comprising the integrated circuit of any of
claims 1 to 11. - Embodiments of this disclosure will be described hereinafter, by way of example only, with reference to the accompanying drawings in which like reference signs relate to like elements and in which:
-
Figure 1 shows a balun according to an embodiment of this disclosure; -
Figure 2 shows a balun according to another embodiment of this disclosure; -
Figures 3-5 show the various metal layers of a balun according to an embodiment of this disclosure; -
Figure 6 shows some of the metal layers of a balun according to another embodiment of this disclosure; -
Figure 7 shows a balun; -
Figure 8 models the phase imbalance, amplitude imbalance and CMRR of the balun ofFigure 7 ; -
Figure 9-10 show a network analysis of a balun according to an embodiment of this disclosure; -
Figure 11 models the phase imbalance, amplitude imbalance and CMRR of a balun of the kind shown inFigure 1 ; -
Figure 12 models the phase imbalance, amplitude imbalance and CMRR of a balun of the kind shown inFigure 2 ; -
Figure 13 models the phase imbalance, amplitude imbalance and CMRR of a balun of the kind shown inFigure 1 , which is provided also with a patterned ground shield; and -
Figure 14 models the phase imbalance, amplitude imbalance and CMRR of a balun of the kind shown inFigure 2 , which is provided also with a patterned ground shield. - Embodiments of this disclosure are described in the following with reference to the accompanying drawings.
-
Figure 1 shows abalun 10 according to an embodiment of this disclosure. Thebalun 10 is provided on an integrated circuit. The integrated circuit comprises a semiconductor substrate, which may for instance comprise silicon. Further details of the construction and manufacture of abalun 10 of the kind disclosed herein will be set out below in relation toFigures 3 to 6 . - The
balun 10 inFigure 1 includes aprimary inductor coil 14 and asecondary inductor coil 12. Theprimary inductor coil 14 has a first end and a second end, with a number of windings located in-between. The first end of theprimary inductor coil 14 is coupled to areference voltage 20. Typically, thereference voltage 20 may be ground. The second end of theprimary inductor coil 14 forms a singleended input 6 of the balun. Thesecondary inductor coil 12 has a first end and a second end, which form adifferential output balun 10. The capacitance between the ends of theprimary inductor coil 14 and thesecondary inductor coil 12 are represented inFigure 1 by thecapacitances - In accordance with embodiments of this disclosure, the
secondary inductor coil 12 is provided with acenter tap 11. Thecenter tap 11 is typically provided at a point located midway along the turn(s) between the first end and the second end of thesecondary inductor coil 12. Thecenter tap 11 may thus form a virtual ground node of thesecondary inductor coil 12. Thecenter tap 11 is coupled to areference voltage 30. Typically, thereference voltage 30 may be ground. In particular, and as shown inFigure 1 , thecenter tap 11 is coupled to thereference voltage 30 via acapacitance 40. The coupling of acenter tap 11 of thesecondary inductor coil 12 to a reference voltage via thecapacitance 40 in this way can allow a common mode rejection ratio (CMRR) of thebalun 10 to be tuned. This may be achieved by, for instance, selecting the value of the capacitance. Accordingly, the performance of the device may be improved. - In some embodiments, the
capacitance 40 may be implemented as a separate capacitor component having first and second capacitor plates, coupled between thecenter tap 11 and thereference voltage 30. In such embodiments, tuning the CMRR may be achieved conveniently by choosing the capacitance value of the separate capacitor component. - In some embodiments, the
capacitance 40 may be implemented using a ground shield of thebalun 10. The ground shield is typically located on or in the semiconductor substrate (e.g. adjacent to (e.g. beneath) theprimary inductor coil 14 and the secondary inductor coil 12). The ground shield in such embodiments is connected to the virtual ground node provided by thecenter tap 11. The use of a ground shield in this way can simultaneously provide electromagnetic (EM) shielding for thebalun 10 and tuning of the CMRR by configuring (e.g. the shape and size of) the ground shield to select the capacitance that it provides. The provision of a ground shield of this kind will be described in more detail below in relation toFigure 6 . - It is envisaged that the
capacitance 40 may be implemented using a combination of a ground shield and a separate capacitor component as noted above. -
Figure 2 shows abalun 10 according to another embodiment of this disclosure. Thebalun 10 inFigure 2 is similar to thebalun 10 shown inFigure 1 , and only the differences will be described below. - The
balun 10 inFigure 2 is provided with acapacitance 42. In this embodiment, the first end of theprimary inductor coil 14 is coupled to thereference voltage 20 via thecapacitance 42. Thecapacitance 42 may be implemented as a separate capacitor component having first and second capacitor plates, coupled between the first end of theprimary inductor coil 14 and thereference voltage 20. In such embodiments, further tuning of the CMRR may be achieved conveniently by choosing the capacitance value of the separate capacitor component. The CMRR tuning in the embodiment ofFigure 2 may thus be provided by a combination of thecapacitance 40 and thecapacitance 42. As noted above, thecapacitance 40 may be implemented as a separate capacitor component and/or by a ground shield. -
Figures 3-5 show the various metal layers of abalun 10 according to an embodiment of this disclosure. Theprimary inductor coil 14 and thesecondary inductor coil 12 described above may be implemented as patterned metal features located in ametallization stack 100 on a major surface of the semiconductor substrate of the integrated circuit. As is known in the art of semiconductor manufacturing, metallization stacks typically include a plurality of metal layers including lithographically patterned metal features. Thestack 100 typically also includes via layers, which are sandwiched between the metal layers. The via layers include electrically conductive vias, for interconnecting the patterned metal features located in the neighbouring metal layers. - In the example of
Figures 3 to 5 , themetallization stack 100 includes at least six metal layers (M1, M2, M3, M4, M5, M6) and intervening via layers (VI, V2, V3, V4, V5). Theprimary inductor coil 14 and thesecondary inductor coil 12 are implemented in metal layers M4, M5 and M6.Figure 3 shows the patterned metal features located in metal layer M4, plus the features located in the via layer (V4) between M4 and M5.Figure 4 shows the patterned metal features located in metal layer M5, plus the features located in the via layer (V5) between M5 and M6.Figure 5 shows the patterned metal features located in metal layer M6, plus (again) the features located in the via layer (V5) between M5 and M6. - In
Figure 3 , themetal feature 52 forms the part of thesecondary inductor coil 12 located in M4 and V4. The metal features 54 form the differential output of the balun. The metal features 56 is located in via layer V4 and connect thefeatures 54 to corresponding features in metal layer M5. - In
Figure 4 ,metal feature 62 forms the part of thesecondary inductor coil 12 located in M5.Metal feature 64 forms the part of theprimary inductor coil 14 located in M5.Metal feature 69A forms a first end of theprimary inductor coil 14, which may be coupled to a reference voltage.Metal feature 69B forms a second end of theprimary inductor coil 14, which forms the single ended input of the balun. Metal features 67, which are located in via layer V5, connect the features of theprimary inductor coil 14 in M5 to the features of theprimary inductor coil 14 in M6. Metal features 66, which are located in via layer V5, connect the features of thesecondary inductor coil 12 in M5 to the features in metal layer M6. Metal features 68 form the differential output of the balun (along with thefeatures 54 shown inFigure 3 ). - In
Figure 5 , themetal feature 70 forms the part of thesecondary inductor coil 12 located in M6. Themetal feature 72 forms the part of theprimary inductor coil 14 located in M6. Metal features 66 located in via layer V5 (described above in relation toFigure 4 ) are also visible inFigure 5 .Metal feature 74 forms a ground reference ring around the structure, which have the purpose of defining the input and output common-mode ground potential both at the primary and secondary inductor coil positions. -
Figure 6 shows, in addition to the features ofFigure 5 , the optional provision of a patterned ground shield formed bymetal feature 110. Themetal feature 110 forming the ground shield may be provided adjacent theprimary inductor coil 14 and thesecondary inductor coil 12. For instance, as shown inFigure 6 , themetal feature 110 forming the ground shield is provided beneath theprimary inductor coil 14 and thesecondary inductor coil 12. - As noted above, in some embodiments, the
capacitance 40 of thebalun 10 may be implemented at least in part by a ground shield.Figure 6 shows some of the metal layers of a balun according to another embodiment of this disclosure, in which such aground shield 110 is included. Note that the features of theprimary inductor coil 14, thesecondary inductor coil 12, thecenter tap 11 and so on in this embodiment may be substantially as already described above in relation toFigure 3 to 5 . - The
ground shield 110 may be provided in a metal layer of a via layer of themetallization stack 100. As can be appreciated fromFigure 6 , for effective shielding of the features of thebalun 10, the ground shield in this embodiment is located beneath the primary 14 and secondary 12 inductor coils. For instance, when viewed from above the major surface of the substrate upon which themetallization stack 100 is provided, the turns of the primary 14 and secondary 12 inductor coils may be located within an outer peripheral edge of theground shield 110. - According to an embodiment of the present disclosure, a method of making integrated circuit may include the following steps. The method includes providing a semiconductor substrate. As noted above, the substrate may, for instance, be a silicon substrate. It is envisaged that the substrate may comprise part of a larger wafer, which may subsequently be singulated (diced), for manufacturing a plurality of like integrated circuits, each including a balun according to the present disclosure.
- The substrate may, as part of the back end of line (BEOL) manufacturing process, be provided with a
metallization stack 100. Thestack 100 may include features for interconnecting components of the integrated circuit located in the substrate and for providing input/output terminals to the substrate. As described herein, themetallization stack 100 may also include patterned metal features implementing thebalun 10. - Accordingly, the method may also include forming a balun on a major surface of the substrate. This may be done by using BEOL metallization techniques to form the
primary inductor coil 14 and thesecondary inductor coil 12, thecenter tap 11 andoptional ground shield 110. As noted above, theprimary inductor coil 14 has a first end and a second end. The first end of theprimary inductor coil 14 is coupled to a reference voltage, which may be ground. For instance, the first end of theprimary inductor coil 14 may be coupled to a ground terminal of the substrate. The second end of theprimary inductor coil 14 forms a single ended input of the balun. As also noted above, thesecondary inductor coil 12 has a first end and a second end, which form the differential output of thebalun 10. The secondary inductor coil also has acenter tap 11 coupled to a reference voltage via a capacitance for tuning a common mode rejection ratio of thebalun 10. Again, the reference voltage may be ground (e.g. the capacitance may be coupled to a ground terminal of the substrate). - Where the
capacitances -
Figure 7 shows a balun, andFigure 8 models the phase imbalance, amplitude imbalance and CMRR of the balun ofFigure 7 . - In
Figure 7 , the second end of the primary inductor coil (i.e. the end that forms the single ended input) of the balun is labelled asterminal 1, the first end of the secondary inductor coil of the balun is labelled asterminal 2, and the second end of the secondary inductor coil of the balun is labelled as terminal 3. The inductance of the primary inductor coil may be denoted as Lp, and the inductance of the secondary inductor coil may be denoted as Ls. Ls includes two contributions Ls/2, each from a respective part of the secondary inductor coil that is located on either side of the center tap. The capacitance between the primary inductor coil and the secondary inductor coil of the balun is represented by the capacitances Cp. -
- Turning to
Figure 8 , the upper graph models thephase imbalance 80 and theamplitude imbalance 81 of the balun ofFigure 7 , while the lower graph models theCMRR 82. As may be appreciated fromFigure 8 , the balun ofFigure 7 exhibits imperfect imbalance and limited CMRR. -
Figure 9-10 show a network analysis of a balun according to an embodiment of this disclosure. - The CMRR of the balun may be converted from s- to z-parameters (see S. Aloui, et al., "High-Gain and Linear 60-GHz Power Amplifier With a Thin Digital 65-nm CMOS Technology," IEEE Trans. on MTT, vol. 61, no. 6, pp. 2425-2437, June 2013):
-
- To reach high CMRR_Z, the condition Z31 + Z21 may be satisfied.
- In the ideal model, this goal may be reached by adding a compensation capacitor (CCM) for the common-mode signals (note that in
Figure 10 the balun is modeled by two mutually coupled inductors L1 and L2). -
-
- This solution has been checked by simulations in which it has been found that the solution is also valid for the non-simplified model (i.e. it is valid for both the right hand side circuit and the left hand side circuit shown in
Figure 9 ). - Turning to
Figure 11 , the upper graph models thephase imbalance 83 and theamplitude imbalance 84 of a balun of the kind shown inFigure 1 , which includes acenter tap 11 provided at a point located midway along the turn(s) between the first end and the second end of thesecondary inductor coil 12, and in which thecenter tap 11 is coupled to ground via acapacitance 40. The lower graph inFigure 11 models CMRR Z 85 andCMRR 86 of thebalun 10. Thecapacitance 40 of thebalun 10 modelled inFigure 11 comprises a separate capacitor component as noted above. As may be appreciated fromFigure 11 , a balun according to an embodiment of this invention has an improved balance and an improved CMRR (>34dB and the bandwidth of the device). In accordance with an embodiment of this disclosure, a particular bandwidth of interest is in the range 26-30 GHz. - Turning to
Figure 12 , the upper graph models thephase imbalance 87 and theamplitude imbalance 88 of a balun of the kind shown inFigure 2 , which includes acenter tap 11 provided at a point located midway along the turn(s) between the first end and the second end of thesecondary inductor coil 12, in which thecenter tap 11 is coupled to ground via acapacitance 40, and in which the first end of theprimary inductor coil 14 is coupled to areference voltage 20 via thecapacitance 42. The lower graph inFigure 12 models CMRR_Z 89 andCMRR 90 of thebalun 10. Thecapacitances balun 10 modelled inFigure 12 each comprise a separate capacitor component as noted above. As may be appreciated fromFigure 12 , a balun according to an embodiment of this invention has a further improved balance and a further improved CMRR (>42dB and the bandwidth of the device). Again, in accordance with an embodiment of this disclosure, a particular bandwidth of interest is in the range 26-30 GHz. - Turning to
Figure 13 , the upper graph models thephase imbalance 91 and theamplitude imbalance 92 of a balun of the kind shown inFigure 1 , which includes acenter tap 11 provided at a point located midway along the turn(s) between the first end and the second end of thesecondary inductor coil 12, and in which thecenter tap 11 is coupled to ground via acapacitance 40. The lower graph inFigure 13 models CMRR_Z 93 andCMRR 94 of thebalun 10. Thecapacitance 40 of thebalun 10 modelled inFigure 13 comprises a combination of separate capacitor component and aground shield 110 of the kind described above in relation toFigure 6 . As may be appreciated fromFigure 13 , a balun according to an embodiment of this invention has a yet further improved balance and a yet further improved CMRR (>40dB and the bandwidth of the device). Again, in accordance with an embodiment of this disclosure, a particular bandwidth of interest is in the range 26-30 GHz. - Turning to
Figure 14 , the upper graph models thephase imbalance 95 and theamplitude imbalance 96 of a balun of the kind shown inFigure 2 , which includes acenter tap 11 provided at a point located midway along the turn(s) between the first end and the second end of thesecondary inductor coil 12, in which thecenter tap 11 is coupled to ground via acapacitance 40, and in which the first end of theprimary inductor coil 14 is coupled to areference voltage 20 via thecapacitance 42. The lower graph inFigure 14 models CMRR_Z 97 andCMRR 98 of thebalun 10. Thecapacitance 40 of thebalun 10 modelled inFigure 14 comprises a combination of separate capacitor component and aground shield 110 of the kind described above in relation toFigure 6 . Thecapacitance 42 of thebalun 10 modelled inFigure 14 comprises a separate capacitor component as noted above. As may be appreciated fromFigure 14 , a balun according to an embodiment of this invention also has a yet further improved balance and a yet further improved CMRR (>50dB and the bandwidth of the device). Again, in accordance with an embodiment of this disclosure, a particular bandwidth of interest is in the range 26-30 GHz. - In integrated circuit including a
balun 10 of the kind described above may have a number of applications. For instance, in some embodiments there may be provided a differential transceiver (e.g. for operation at RF and mmWave frequencies) including an integrated circuit having abalun 10 of the kind described above. Such a differential transceiver may be provided in mobile or fixed network systems. In another embodiment, there may be provided a power amplifier (PA) including an integrated circuit having abalun 10 of the kind described above, in which thebalun 10 operates as an output balun of the power amplifier. In a further embodiment, there may be provided a low noise amplifier (LNA) including an integrated circuit having abalun 10 of the kind described above, in which the balun operates as an input balun of the low noise amplifier. - Accordingly, there has been described an integrated circuit and a method of making the same. The integrated circuit includes a semiconductor substrate. The integrated circuit also includes a balun. The balun includes a primary inductor coil having a first end and a second end. The first end of the primary inductor coil is coupled to a reference voltage. A second end of the primary inductor coil forms a single ended input of the balun. The balun also includes a secondary inductor coil having a first end and a second end. The first end and the second end form a differential output of the balun. The secondary inductor coil has a center tap coupled to a reference voltage via a capacitance for tuning a common mode rejection ratio of the balun.
- Although particular embodiments of this disclosure have been described, it will be appreciated that many modifications/additions and/or substitutions may be made within the scope of the claims.
Claims (15)
- An integrated circuit comprising:a semiconductor substrate; anda balun comprising:a primary inductor coil having a first end and a second end, wherein the first end of the primary inductor coil is coupled to a reference voltage, and wherein the second end of the primary inductor coil forms a single ended input of the balun; anda secondary inductor coil having a first end and a second end, wherein the first end and the second end form a differential output of the balun, and wherein the secondary inductor coil has a center tap coupled to a reference voltage via a capacitance for tuning a common mode rejection ratio of the balun.
- The integrated circuit of claim 1, wherein the capacitance for tuning a common mode rejection ratio of the balun comprises a capacitor component having first and second capacitor plates.
- The integrated circuit of claim 1 or claim 2, wherein the capacitance for tuning a common mode rejection ratio of the balun comprises a ground shield located on or in the semiconductor substrate.
- The integrated circuit of claim 3, wherein the ground shield is located adjacent the primary and secondary inductor coils.
- The integrated circuit of claim 3 or claim 4, wherein the ground shield is coupled to the center tap of the secondary inductor coil.
- The integrated circuit of any preceding claim, wherein the first end of the primary inductor coil is coupled to said reference voltage via a capacitance for tuning a common mode rejection ratio of the balun.
- The integrated circuit of any preceding claim, wherein the primary inductor coil and the secondary inductor coil comprise patterned metal features located in a metallization stack on a major surface of the semiconductor substrate.
- The integrated circuit of claim 7, when dependent upon any of claims 3 to 5, wherein the ground shield comprises a patterned metal feature located in a metal layer of the metallization stack.
- The integrated circuit of any preceding claim, wherein the center tap forms a virtual ground node of the secondary inductor coil.
- The integrated circuit of any preceding claim, wherein the reference voltage to which the center tap of the secondary inductor coil is coupled via said capacitance is ground.
- The integrated circuit of any preceding claim, wherein the reference voltage to which the first end of the primary inductor coil is coupled is ground.
- A differential transceiver comprising the integrated circuit of any preceding claim.
- A power amplifier comprising the integrated circuit of any of claims 1 to 11.
- A low noise amplifier comprising the integrated circuit of any of claims 1 to 11.
- A method of making an integrated circuit, the method comprising:providing a semiconductor substrate; andforming a balun on a major surface of the substrate by:forming a primary inductor coil having a first end and a second end, wherein the first end of the primary inductor coil is coupled to a reference voltage, and wherein the second end of the primary inductor coil forms a single ended input of the balun; andforming a secondary inductor coil having a first end and a second end, wherein the first end and the second end form a differential output of the balun, and wherein the secondary inductor coil has a center tap coupled to a reference voltage via a capacitance for tuning a common mode rejection ratio of the balun.
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EP18212964.3A EP3671775A1 (en) | 2018-12-17 | 2018-12-17 | Integrated circuit comprising a balun |
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EP18212964.3A EP3671775A1 (en) | 2018-12-17 | 2018-12-17 | Integrated circuit comprising a balun |
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Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20060202776A1 (en) * | 2005-03-11 | 2006-09-14 | Samsung Electronics Co., Ltd. | On-chip balun and transceiver using the same and method for fabricating on-chip balun |
US20090195324A1 (en) * | 2008-02-04 | 2009-08-06 | Freescale Semiconductor, Inc. | Balun transformer with improved harmonic suppression |
US20170287618A1 (en) * | 2016-03-30 | 2017-10-05 | Stmicroelectronics Sa | Power transformer of the symmetric-asymmetric type with a fully-balanced topology |
US20180062607A1 (en) * | 2016-08-31 | 2018-03-01 | Analog Devices Global | Switchable transformer-based balun |
-
2018
- 2018-12-17 EP EP18212964.3A patent/EP3671775A1/en not_active Withdrawn
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
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US20060202776A1 (en) * | 2005-03-11 | 2006-09-14 | Samsung Electronics Co., Ltd. | On-chip balun and transceiver using the same and method for fabricating on-chip balun |
US20090195324A1 (en) * | 2008-02-04 | 2009-08-06 | Freescale Semiconductor, Inc. | Balun transformer with improved harmonic suppression |
US20170287618A1 (en) * | 2016-03-30 | 2017-10-05 | Stmicroelectronics Sa | Power transformer of the symmetric-asymmetric type with a fully-balanced topology |
US20180062607A1 (en) * | 2016-08-31 | 2018-03-01 | Analog Devices Global | Switchable transformer-based balun |
Non-Patent Citations (1)
Title |
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S. ALOUI ET AL.: "High-Gain and Linear 60-GHz Power Amplifier With a Thin Digital 65-nm CMOS Technology", IEEE TRANS. ON MTT, vol. 61, no. 6, June 2013 (2013-06-01), pages 2425 - 2437, XP011511905, DOI: doi:10.1109/TMTT.2013.2258169 |
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