Transformer circuits, amplifier circuits, oscillator circuits, and integrated circuits

Abstract

A transformer circuit, an amplifier circuit, an oscillator circuit, and an integrated circuit are provided. The transformer circuit includes: a transformer having a primary coil and a secondary coil, the primary coil having a first primary terminal and a second primary terminal, and the secondary coil having a first secondary terminal and a second secondary terminal; and a secondary coil driver configured to drive a secondary voltage signal V2 between the secondary terminals, the secondary voltage signal V2 having a target relationship with a primary voltage signal V1 between the primary terminals driven by the primary coil driver, so that an inductance value measured between the primary terminals is controlled by the target relationship.

Description

Technical Field

[0001] The present invention relates to transformer circuits used, for example, as impedances (inductors). In particular, the present invention relates to such transformer circuits whose impedance value (inductance) can be varied or "tuned". Background Art

[0002] For example, one possible application of such a transformer circuit may be in a tuned amplifier having applications in circuits such as low noise amplifier (LNA) circuits, video graphics array (VGA) circuits, clock buffer circuits, and voltage controlled oscillator (VCO) buffer circuits in phase locked loops (PLLs). Example implementations of PLLs including such VCOs include analog-to-digital converters (ADCs), digital-to-analog converters (DACs), serializer / deserializer (SERDES) circuits, clock and data recovery (CDR) circuits, wireless transceivers, and processor clock circuits.

[0003] As background technology, reference will now be made to Figure 1 Consider the schematic diagram of a conventional resistive load amplifier 10 to explore just one potential application of the present invention. The resistive load amplifier 10 is a transconductance (G m ) amplifier, which is configured to receive an input voltage signal (such as a differential clock signal having an AC component) between its input terminals Vin+ and Vin- and output a current proportional to the AC input voltage signal. L Connected between the amplifier 10 and the voltage source VDD, so that the amplifier 10 drives the resistive load R through the output current L A differential output voltage signal is generated between the output terminals Vout+ and Vout-. The resistive load amplifier 10 exhibits a low-pass frequency response with a maximum operating frequency which is limited by the resistive load R L and the electrode limitations caused by parasitic capacitances present at nodes Vout+ and Vout-. Figure 1 The maximum operating frequency of the conventional resistive load amplifier is shown. The resistive load can be replaced by an inductive load.

[0004] Figure 2 FIG. 2 is a schematic diagram of a conventional inductive load amplifier 20. The inductive load amplifier 20 is Figure 1 The resistive load amplifier operates in the same way, but the resistive load R L is replaced by an inductive load L. The inductive load L is tuned to resonate with the (discrete and / or parasitic) capacitances C1, C2 present at the nodes Vout+ and Vout- to obtain the desired frequency of the output voltage signal. The resulting amplifier is able to produce high gain at the desired frequency.

[0005] Despite the provision of such an inductively loaded amplifier 20, it has been found that previously considered inductively loaded amplifiers 20 suffer from a narrow bandwidth passband frequency response. Furthermore, the range over which the center frequency (ie, resonant frequency) of such an inductively loaded amplifier 20 can be tuned is very limited.

[0006] It would be desirable to address some or all of the above-mentioned problems. Summary of the invention

[0007] According to an embodiment of the first aspect of the present invention, a transformer circuit is provided, which includes: a transformer having a primary coil and a secondary coil, the primary coil having a first primary terminal and a second primary terminal, and the secondary coil having a first secondary terminal and a second secondary terminal; and a secondary coil driver, which is configured to drive a secondary voltage signal V2 between the secondary terminals, and the secondary voltage signal V2 has a target relationship with a primary voltage signal V1 between the primary terminals driven by the primary coil driver, so that the inductance value measured between the primary terminals is controlled by the target relationship.

[0008] Therefore, the inductance value measured between the primary terminals can be controlled by driving the secondary voltage signal V2 between the secondary terminals according to the target relationship. The target relationship between the primary voltage signal V1 and the secondary voltage signal V2 is a relationship that can produce a specific frequency for the primary voltage signal V1 (for example, the inductance measured between the primary terminals forms a part of a resonant circuit of an oscillator circuit, such as an LC resonant circuit). That is, the inductance measured between the primary terminals is controlled based on the target relationship.

[0009] The primary output voltage V1 may be referred to as the output voltage of the primary coil driver. In embodiments where the primary coil driver is a relevant portion of a transconductance amplifier, the primary voltage signal V1 may be considered to be the output voltage of the relevant portion of the transconductance amplifier. Alternatively, in embodiments where the primary coil driver is a relevant portion of a voltage controlled oscillator, the primary voltage signal V1 may be considered to be the output voltage of the relevant portion of the voltage controlled oscillator (VCO), for example defined by a differential output oscillator signal of the VCO.

[0010] The driving of the secondary voltage signal V2 by the secondary coil driver may be referred to as forcing or generating the secondary voltage signal V2 to be a specific voltage signal that is a scaled version of the primary voltage signal V1 in magnitude (i.e., voltage). The target relationship may be a proportionality factor between the primary voltage signal V1 and the secondary voltage signal V2 that produces a desired inductance measured between the primary coils.

[0011] Similarly, the driving of the primary voltage signal V1 by the primary coil driver may be referred to as generating the primary voltage V1 based on an input to the primary coil driver (eg, from an external source).

[0012] The target relationship may be that the secondary voltage signal V2 is substantially proportional to the primary voltage signal V1 (in magnitude). The scaling factor may define a substantially proportional relationship between the two voltage signals V1, V2. For example, the primary voltage signal V1 and the secondary voltage signal V2 may be substantially the same, in which case the scaling factor would be 1:1, or the primary voltage signal V1 and the secondary voltage signal V2 may be substantially proportional to each other, such that the primary voltage signal V1 is scaled by the scaling factor (e.g., between 0 and 1, or between -1 and 1) to produce the secondary voltage signal V2.

[0013] The secondary coil driver may be configured to control the driven secondary voltage signal V2 based on the primary voltage signal V1 to maintain a target relationship. As discussed above, the driving of the secondary voltage signal V2 may be referred to as forcing or generating the secondary voltage signal V2 to be a specific voltage signal that is a scaled version of the primary voltage signal V1 according to a desired target relationship (e.g., in the case of an oscillator circuit, a target relationship that may produce, for example, a desired primary voltage signal V1 frequency).

[0014] The primary coil may be electrically connected to the secondary coil via a secondary coil driver, and / or the secondary coil driver may be electrically connected to the primary coil and / or the primary coil driver. The electrical connection may be a conductive path that allows current to flow between the primary coil and the secondary coil. Alternatively, the electrical connection may be a conductive path comprising one or more active components (e.g., a transistor), the conductive path allowing current to flow between the primary coil and the secondary coil via the active components. Alternatively, the electrical connection may be a conductive path comprising an electrostatic connection (e.g., due to a capacitor being inserted into the conductive path), the conductive path allowing current (a signal having an AC component) to flow between the primary coil and the secondary coil via the electrostatic connection.

[0015] The secondary coil driver may include an amplifier connected between the primary coil and the secondary coil, the amplifier being configured to generate a secondary voltage signal V2 based on the primary voltage signal V1 so that a target relationship is V2∝V1×A, where A is an amplification factor. The amplifier may be a voltage amplifier configured to amplify the primary voltage signal V1 by the amplification factor according to the target relationship to generate the secondary voltage signal V2.

[0016] Alternatively, the magnification factor may be referred to as a scaling factor.

[0017] The secondary coil driver may be configured to control the amplification factor A based on the control signal to control the target relationship. The control signal may be received from an external source such as an external controller or a user interface. The control signal may be an alternating current (AC) signal having a DC component.

[0018] The amplifier may include a first sub-amplifier and a second sub-amplifier, the first sub-amplifier being connected between the first primary terminal and the first secondary terminal, and the second sub-amplifier being connected between the second primary terminal and the second secondary terminal. The sub-amplifiers may apply the same amplification factor as each other.

[0019] The first sub-amplifier and the second sub-amplifier may be configured to amplify components of the primary voltage signal V1. For example, the first sub-amplifier may amplify the positive component of the primary voltage signal V1, and the second sub-amplifier may amplify the negative component of the primary voltage signal V1.

[0020] The first control signal may control the first sub-amplifier, and the second control signal may control the second sub-amplifier.

[0021] The first primary terminal may be electrically connected to the first secondary terminal via the first sub-amplifier, and the second primary terminal may be electrically connected to the second secondary terminal via the second sub-amplifier. As discussed above, the electrical connection may be a conductive path including one or more active components (e.g., a transistor), and may also include an electrostatic connection for transferring an AC component of a signal (e.g., due to a capacitor being inserted into the conductive path).

[0022] The secondary coil driver may be implemented as a primary coil driver and a capacitor network (as an example of a passive impedance network) connected between the primary coil and the secondary coil, the capacitor network being configured to apply a scaled version of the primary voltage signal V1 to the secondary coil as the secondary voltage signal such that the target relationship is V2∝V1×S, where S is a scaling factor. The capacitor network may be configured to scale the primary voltage signal V1 by the scaling factor according to the target relationship to generate a secondary voltage signal V2.

[0023] The capacitor network may include a varactor diode, and the secondary coil driver may be configured to control a scaling factor S based on a tuning voltage applied to the secondary coil to control the target relationship.

[0024] The capacitor network may include a first capacitive voltage divider and a second capacitive voltage divider (as an example of a passive impedance voltage divider or just a voltage divider), the first capacitive voltage divider being connected so that the voltage signal applied at the first secondary terminal depends on the voltage signal applied at the first primary terminal, and the second capacitive voltage divider being connected so that the voltage signal applied at the second secondary terminal depends on the voltage signal applied at the second primary terminal. Thus, the target relationship may be obtained by using a capacitor network instead of an amplifier to scale the primary voltage signal V1 by a proportional factor to produce a secondary voltage signal V2.

[0025] Each capacitive voltage divider may include a first capacitor and a second capacitor connected in series, such that the first capacitor of each capacitive voltage divider is connected between a first node and an intermediate node of the voltage divider, and the second capacitor of each capacitive voltage divider is connected between the intermediate node and a second node of the voltage divider. For the first capacitive voltage divider, the first node is connected to the first primary terminal and the intermediate node is connected to the first secondary terminal, and for the second capacitive voltage divider, the first node is connected to the second primary terminal and the intermediate node is connected to the second secondary terminal.

[0026] For the first capacitive voltage divider and the second capacitive voltage divider, the second node may be connected to a voltage source node.

[0027] For the first capacitive voltage divider, the second node may be connected to the second primary terminal, and for the second capacitive voltage divider, the second node may be connected to the first primary terminal.

[0028] For at least one of the capacitive voltage dividers, at least one of the capacitors is a variable capacitor, and wherein the second coil driver is configured to control the capacitance value of the at least one variable capacitor based on the control signal to control the target relationship, or for at least one of the capacitive voltage dividers, at least one of the capacitors is a varactor diode, and wherein the second coil driver is configured to control a tuning voltage applied to the second coil based on the control signal to control the target relationship. The tuning voltage can be applied to the center tap of the secondary coil. In addition, the tuning voltage can be connected to a fixed potential such as an external voltage source.

[0029] The first primary terminal can be electrically connected to the first secondary terminal via a first capacitive voltage divider, and the second primary terminal can be electrically connected to the second secondary terminal via a second capacitive voltage divider. As discussed above, the electrical connection can be a conductive path including an electrostatic connection (e.g., due to a capacitor being inserted into the conductive path), i.e., a conductive path that provides AC coupling and DC decoupling.

[0030] The primary coil driver may be part of an amplifier or part of an oscillator. For example, the primary coil driver may include a part of an amplifier or an oscillator that outputs an output voltage.

[0031] According to an embodiment of the second aspect of the present invention, a transformer circuit is provided, which includes: a transformer having a primary coil and a secondary coil, the primary coil having a first primary terminal and a second primary terminal, and the secondary coil having a first secondary terminal and a second secondary terminal; and a secondary coil controller, which is configured to selectively short-circuit or open-circuit the secondary coil to control the inductance value measured between the primary terminals.

[0032] According to an embodiment of the third aspect of the present invention, there is provided an amplifier circuit, which includes a transformer circuit of any of the above-mentioned aspects, optionally wherein the amplifier is an inductive load amplifier circuit and the transformer forms an inductive load of the inductive load amplifier circuit.

[0033] According to an embodiment of a fourth aspect of the present invention, there is provided an oscillator circuit comprising the transformer circuit of any of the above-mentioned aspects.

[0034] According to an embodiment of a fifth aspect of the present invention, there is provided an integrated circuit, such as an IC chip, comprising any of the transformer circuit, amplifier circuit or oscillator circuit as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Reference will now be made by way of example to the accompanying drawings, in which:

[0036] The above considerations Figure 1 is a schematic diagram of a resistive load amplifier;

[0037] The above considerations Figure 2 is a schematic diagram of an inductive load amplifier;

[0038] Figure 3 is a schematic diagram of a transformer circuit implementing the present invention;

[0039] Figure 4 Yes means Figure 3 a schematic diagram of an equivalent circuit of a portion of the transformer circuit shown;

[0040] Figure 5 is a schematic diagram of another transformer circuit implementing the present invention;

[0041] Figure 6 is corresponding to Figure 5 A schematic diagram of an equivalent circuit of the transformer circuit shown;

[0042] Figure 7is a schematic diagram of another transformer circuit implementing the present invention;

[0043] Figure 8 is a schematic diagram of another transformer circuit implementing the present invention;

[0044] Fig. 9 is a schematic diagram of another transformer circuit implementing the present invention;

[0045] Fig.10 is a schematic diagram of another transformer circuit implementing the present invention;

[0046] Fig.11 is a schematic diagram of another transformer circuit implementing the present invention;

[0047] Fig.12 is a schematic diagram of a voltage controlled oscillator including a transformer embodying the present invention;

[0048] Fig.13 is a schematic diagram of an integrated amplifier circuit including a transformer embodying the present invention;

[0049] Fig.14 is a schematic diagram of an integrated phase-locked loop circuit including a transformer embodying the present invention; and

[0050] Fig.15 It includes implementation Fig.14 Schematic diagram of a transformer-integrated ADC or DAC circuit with a phase-locked loop. DETAILED DESCRIPTION

[0051] Figure 3 is a schematic diagram of a transformer circuit 100 implementing the present invention. The transformer circuit 100 can be used to replace Figure 2 The inductor L of the conventional inductively loaded amplifier 20 is shown to increase the frequency tuning range.

[0052] The transformer circuit 100 includes a primary coil 110 magnetically coupled to a secondary coil 120 to form a transformer. For example, while the primary coil 110 and the secondary coil 120 may be coupled via a magnetic core such as silicon steel or solid iron, air coupling is also possible such that magnetic coupling is facilitated by the permeability of air in free space. In the case of an integrated circuit implemented on an IC chip (as is the focus of the present invention), the primary coil 110 and the secondary coil 120 may be implemented, for example, in adjacent metal layers of the IC chip with a dielectric layer therebetween.

[0053] The switch 140 connected to the secondary coil 120 is operable in an open position, in which the inductance measured between the output terminals Vout+ and Vout- effectively becomes L 1The switch 140 is also operable in a closed position, in which the inductance measured between the output terminals Vout+ and Vout- comprises L 1 and L 2 effect (as described in more detail later in this article).

[0054] The primary coil driver 130 is connected to the primary coil 110 to generate or drive a primary voltage across the primary coil 110. The voltage generated across the primary coil 110 is output from the output terminals Vout+ and Vin+ and has an AC component (and may be an AC signal). According to some embodiments of the present invention, the primary coil driver 130 may be configured so that the transformer circuit 100 is, for example, an amplifier circuit or an oscillator circuit.

[0055] exist Figure 4 An equivalent circuit 150 of a portion of the transformer circuit 100 is provided along the relevant portion of the transformer circuit 100 to help illustrate the operation of the transformer circuit 100. The equivalent circuit 150 is based on L 1 -M, L 2 -M and M form shows the equivalent inductance of the transformer circuit 100, where L 1 Represents the primary coil inductance, L 2 represents the inductance of the secondary coil, and M represents the mutual inductance of the primary coil and the secondary coil.

[0056] When the switch 140 is open (ie, the switch is “off”), the equivalent inductance of the transformer portion of the transformer circuit 100 is (L 1 -M)+M=L 1 When the switch 140 is closed (ie, the switch is turned “on”), the equivalent inductance of the transformer 100 becomes It is smaller than L 1 This variation in inductance provides two widely spaced center operating frequencies at which an output voltage signal can be generated and output from the output terminals Vout+ and Vout- (see Figure 3 ) outputs the output voltage signal. In embodiments where the transformer circuit 100 is an amplifier circuit, the switch 140 provides the amplifier with a means for operating at two different frequency bands rather than just one.

[0057] Although the introduction of switch 140 to the secondary coil 120 provides two operating point frequencies, thereby introducing an additional operating frequency band, it is still desirable that the transformer has a continuous frequency tuning range. In addition, due to the parasitic effects introduced by the switching of switch 140 (i.e., through the on-resistance of switch 140), the Q factor of the equivalent inductance of transformer 100 is reduced.

[0058] like Figure 5As shown, according to an embodiment of the present invention, continuous frequency tuning for the transformer may be achieved by replacing the switch 140 of the transformer 100 with the secondary coil driver 240 .

[0059] Figure 5 is a schematic diagram of a transformer circuit 200 embodying the present invention. The transformer circuit 200 includes a primary coil 210 connected to a primary coil driver 230 via a first primary coil terminal 212 and a second primary coil terminal 214, and a secondary coil 220 connected to a secondary coil driver 240 via a first secondary coil terminal 222 and a second secondary coil terminal 224. As before, the primary coil 210 and the secondary coil 220 are coupled to form a transformer.

[0060] like Figure 5 As indicated, the primary coil driver 230 may be considered to be part of the transformer circuit 200. However, in some arrangements, the transformer circuit 200 may be considered to include a circuit provided for connecting to the primary coil driver 230 in addition to the primary coil driver 230. Figure 5 components.

[0061] The present disclosure including other embodiments disclosed later will be understood accordingly. In fact, similar considerations also apply to Figure 3 .

[0062] The primary coil driver 230 is configured to drive a primary voltage signal V1 (an AC voltage signal or a voltage signal having an AC component) between the first primary terminal 212 and the second primary terminal 214 of the primary coil 210 such that a primary current i1 flows through the primary coil 210 .

[0063] The secondary coil driver 240 is configured to drive a secondary voltage signal V2 (an AC voltage signal or a voltage signal having an AC component) between the first secondary terminal 222 and the second secondary terminal 224 of the secondary coil 220 , the secondary voltage signal V2 having a target relationship with the primary voltage signal V1 .

[0064] For ease of explanation, it is assumed that the secondary coil driver 240 drives the secondary voltage signal V2 so that it is substantially proportional to the primary voltage signal V1. For example, it may be V2∝V1×S or V2=V1×S, where S is a proportionality factor.

[0065] As a result, a secondary current i2 proportional to the primary voltage signal V1 flows through the secondary coil 220 , thereby generating a magnetic flux that generates a scaled version αV1 of the primary voltage signal V1 at the primary coil 210 (as a back EMF), where α is also a proportionality factor.

[0066] Figure 62 is a schematic diagram showing an equivalent circuit 250 which represents the transformer circuit 200 but where the primary coil driver 230 is not shown. The effect of the secondary coil driver 240 is shown by the back EMF αV1 which is effectively shown in series with the primary coil 210. Figure 6 The terminals Vout+ and Vout- correspond to Figure 5 Terminals 212 and 214 in. Figure 6 In, L l is the inductance of the primary coil 210, il is the primary current flowing through the primary coil 210, and V l is the primary voltage signal V1.

[0067] Assuming that the secondary coil driver 240 does not exist, so that the reverse EMF αV1 also does not exist, the effect of the secondary coil driver 240 will first be considered by considering the following inductor equation (1):

[0068]

[0069] Now, introducing the effect of the secondary coil driver 240 and thus also the back EMF αV1, it follows that if the voltage signal experienced at the primary coil 210 changes from V l becomes V l -αV l , that is, scaled by 1-α, the current i 1 (or its rate of change) is also scaled by 1-α. Furthermore, it is also obvious from consideration of equation (1) that the current i in the coil actually driven by the primary voltage signal V1 is 1 (or its rate of change) is equivalent to the inductance L by scaling by 1-α. 1 The effective inductance L of the primary coil 210 is scaled by 1 / (1-α) so that E (due to the effect of the back EMF from the secondary coil 220) becomes:

[0070]

[0071] Therefore, according to equation (2), the effective inductance L can be changed by changing the proportionality factor α E , which enables, for example, the resonant frequency / frequency response of the transformer circuit 200 to be changed (tuned), for example, in the case where the transformer circuit 200 is implemented as an oscillator circuit or an amplifier circuit as described above.

[0072] In this example, the scaling factor α depends on the scaling factor S. That is, S is the scaling factor applied to the primary voltage signal V1 to obtain the secondary voltage signal V2 applied to the secondary coil 220, and α is the overall scaling factor of the back EMF. In embodiments where the transformer 200 does not have a 1:1 turns ratio, the scaling factor S and the scaling factor α may not be equal.

[0073] From the above (see equation (2)), it can be concluded that the relationship between V2 and V1 (ie, the proportionality factor S) can be changed or controlled to change or control the effective inductance L of the primary coil 210. E This shows that the effective inductance L E The possibility of controlling to the same resolution as S, and therefore also varying α, is possible, for example to achieve a range of multiple discrete values ​​or even a range of continuous values.

[0074] In addition, Figure 5 The secondary coil driver 240 of the transformer 200 is replaced by Figure 3 The switch 140 in the transformer 100 removes the adverse effect of the on-resistance of the switch 140 on the Q factor. This provides the following advantages: the frequency tuning range is increased without decisively affecting the Q factor of the transformer equivalent inductance.

[0075] Figure 7 2 is a schematic diagram showing a transformer circuit 300 embodying the present invention. The transformer circuit 300 includes a primary coil and a secondary coil configured to operate in the same manner as the primary coil 210 and the secondary coil 220 of the transformer circuit 200. Figure 5 The transformer circuit 200, Figure 6 The illustrated transformer circuit 300 is driven by a primary coil driver (not shown). Figure 5 and Figure 7 The difference between the two sets of transformer circuits shown in is that the secondary coil driver 240 of the transformer circuit 200 is implemented in the form of a (eg, programmable or controllable) amplifier 340 in the transformer circuit 300 .

[0076] The amplifier 340 is electrically connected between the primary coil and the secondary coil, so that the primary voltage signal V1 is fed from the primary coil to the secondary coil via the amplifier 340. For example, the first input terminal of the amplifier 340 can be connected to the first primary terminal and the corresponding output terminal is connected to the first secondary terminal. Similarly, the second input terminal of the amplifier 340 can be connected to the second primary terminal and the corresponding output terminal is connected to the second secondary terminal.

[0077] The amplifier 340 is configured to amplify the primary voltage signal V1 by an amplification factor A to generate a secondary AC voltage signal for driving the secondary coil, such that V2∝V1×A or V2=V1×A, where A is the amplification factor.

[0078] As discussed above, the secondary current i2 proportional to the primary voltage signal V1 flows through the secondary coil, thereby generating a magnetic flux that generates a scaled version αV1 of the primary voltage signal V1 (as a back EMF) at the primary coil 210, where α is a proportionality factor (the variable α is repeatedly used here to simplify the description). Therefore, as described above, according to the above equation (2), the effective inductance L of the primary coil is E (due to the effect of the back EMF from the secondary coil) becomes controllable. Figure 5 The proportional factor S is controlled in a similar way to the amplification factor A to control or change the effective inductance L of the primary coil. E , and the above about Figure 5 The considerations apply mutatis mutandis hereto so that repeated descriptions may be omitted.

[0079] For example, where amplifier 340 is a programmable amplifier, scaling factor α may be adjusted (eg, within a continuous range or within discrete values) by controlling amplification factor A based on an input signal received by amplifier 340. Such an input signal may be received from an external source such as an external controller.

[0080] The amplifier 340 may be an amplifier module electrically connected between the primary coil and the secondary coil. Alternatively, the programmable amplifier may include a first sub-amplifier 342 and a second sub-amplifier 344. The first sub-amplifier 342 may be electrically connected between the first primary terminal and the first secondary terminal and configured to amplify a first component of the primary voltage signal V1. The second sub-amplifier 344 may be electrically connected between the second primary terminal and the second secondary terminal and configured to amplify a second component of the primary voltage signal V1. The first signal component and the second signal component may be, for example, a positive component and a negative component of the primary voltage signal V1.

[0081] In other embodiments of the present invention, a capacitor bank or capacitor network may be used in place of amplifier 340 to achieve voltage scaling. Figure 8 and Fig. 9 An embodiment is shown in which a capacitor is used instead of an amplifier for frequency tuning.

[0082] Figure 8 is a schematic diagram of a transformer circuit 400, wherein: Figure 7The amplifier 340 is replaced by a capacitor network 440. The capacitor network 440 may be considered an example of a passive impedance network (eg, it may include R components, L components, and / or C components), and the present embodiment will be understood as an example accordingly.

[0083] The transformer circuit 400 includes a primary coil and a secondary coil configured to operate in the same manner as the primary coil 210 and the secondary coil 220 of the transformer 200. Figure 5 The transformer circuit 200, Figure 8 The transformer circuit 400 shown is driven by a primary coil driver (not shown). It is also apparent that in this embodiment, the secondary coil driver is implemented as a combination of the primary coil driver and a capacitor network 440 .

[0084] The capacitor network 440 is electrically connected between the primary coil and the secondary coil, so that the primary voltage signal V1 is fed from the primary coil to the secondary coil via the capacitor network 440. For example, the first input terminal of the capacitor network 440 can be connected to the first primary terminal and the corresponding output terminal is connected to the first secondary terminal. Similarly, the second input terminal of the capacitor network 440 can be connected to the second primary terminal and the corresponding output terminal is connected to the second secondary terminal.

[0085] The capacitor network 440 is configured to scale the primary voltage signal V1 by a scaling factor S to generate a secondary voltage signal V2 for driving the secondary coil, such that V2∝V1×S or V2=V1×S, where S is the scaling factor.

[0086] As discussed above, the secondary current i2 proportional to the primary voltage signal V1 flows through the secondary coil, thereby generating a magnetic flux that generates a scaled version αV1 of the primary voltage signal V1 at the primary coil 210 (as a back EMF), where α is a scale factor that depends on the scale factor S (the variable α is reused here to simplify the description). Therefore, as described above, according to the above equation (2), the effective inductance L of the primary coil is E (due to the effect of the back EMF from the secondary coil) becomes controllable. Figure 5 In the example, the effective inductance L of the primary coil can be controlled or changed by controlling the proportional factor S. E , and the above about Figure 5 The considerations also apply here.

[0087] The scaling factor α may be adjusted (e.g., within a continuous range or within discrete values) by controlling the scaling factor S based on, for example, an input signal received from an external source such as an external controller. Such a control signal may, for example, control or program certain capacitors within the capacitor network 440 to adjust the scaling factor S.

[0088] For example, one or more capacitors in capacitor network 440 may be variable capacitors or varactors controlled by corresponding control signals, wherein each of the one or more variable capacitors is configured to change its capacitance, thereby changing the effect of capacitor network 440. The one or more variable capacitors or varactors may be referred to as programmable capacitors.

[0089] In the case of a varactor diode, it is possible to control Figure 8 The tuning voltage V is shown as applied to the center tap between the first secondary terminal and the second secondary terminal of the secondary coil. tune To control the capacitance value. In some embodiments, a switched capacitor may be used in the capacitor network 440, wherein the switched capacitor is programmed to be switched on or off (enter or leave the circuit) using at least one control signal. The switched capacitor may have a fixed capacitance value or may have a variable capacitance value. Advantageously, using a capacitor with a fixed capacitance provides simpler circuit integration and reduces tuning range attenuation. In the case of using a switched capacitor instead of a varactor diode, V tune Can be connected to a fixed voltage potential.

[0090] In some embodiments of the present invention, the capacitor network 440 may include a first capacitive voltage divider 442 and a second capacitive voltage divider 444. Each of the capacitive voltage dividers 442 and 444 may include a first capacitor C connected in series. 1 and the second capacitor C 2 .

[0091] The first capacitor C of the first capacitive voltage divider 442 may be connected 1 and the second capacitor C 2 , so that the second capacitor C 2 is connected between a first voltage source 446 (eg, ground power source, GND) and a first intermediate node 450, and a first capacitor C 1 is connected between the first intermediate node 450 and the first primary terminal. The first intermediate node 450 of the first capacitive voltage divider 442 may be connected to the first secondary terminal of the secondary coil such that the voltage generated at the first secondary terminal is a scaled version of the voltage generated at the first primary terminal.

[0092] The first capacitor C of the second capacitive voltage divider 444 may be connected 1 and the second capacitor C 2 , so that the second capacitor C 2 is connected between a second voltage source 448 (eg, ground power source, GND) and a second intermediate node 452, and a first capacitor C 1The second intermediate node 452 of the second capacitive voltage divider 444 may be connected between the second intermediate node 452 and the second primary terminal. The second intermediate node 452 of the second capacitive voltage divider 444 may be connected to the second secondary terminal of the secondary coil such that the voltage generated at the second secondary terminal is a scaled version of the voltage generated at the second primary terminal.

[0093] The scaling factor S of the transformer circuit 400 may be controlled by the capacitor network 440 and / or the first and second capacitive voltage dividers 442 and 444 to obtain a value of S (or α) between 0 and 1 depending on the resulting voltage drop (or voltage divider effect).

[0094] For example, considering the range of capacitance values ​​between a minimum value (ideally, zero capacitance) and a maximum value (ideally, infinite capacitance), the minimum value can approximate an open circuit connection and the maximum value can approximate a short circuit connection. With this in mind, and referring to Figure 8 , by forming the first capacitor C of the first capacitive voltage divider 442 1 and the first capacitor C of the second capacitive voltage divider 444 1 Both are set to their maximum values, and the second capacitor C of the first capacitive voltage divider 442 is 2 and the second capacitor C of the second capacitive voltage divider 444 2 Both are set to their minimum values, most of the primary voltage signal V1 (ie, the primary voltage signal V1 minus the first capacitor C 1 , C 1 The voltage drop between the two terminals is applied across the secondary coil, which corresponds to an S (or α) value of (close to) 1. 2 and the second capacitor C of the second capacitive voltage divider 444 2 Both are set to their maximum values ​​and the first capacitor C of the first capacitive voltage divider 442 is 1 and the first capacitor C of the second capacitive voltage divider 444 1 Both are set to their minimum values ​​to obtain a S (or α) value (close to) 0. In this way, the secondary coil is connected to the second capacitor C 2 , C 2 The secondary coil is connected to a first voltage source 446 and a second voltage source 448 so that the secondary coil effectively has a DC voltage signal at both of its terminals. Figure 8 As shown, in the present embodiment, the first voltage source 446 and the second voltage source 448 are ground terminals.

[0095] As described above, it should be understood that the scaling factor S (or α) can be controlled to be (close to) any value between 0 and 1 depending on the resolution of the capacitance value.

[0096] In some embodiments, the first capacitor C of the first capacitive voltage divider 442 is 1 and the first capacitor C of the second capacitive voltage divider 444 1 With equal capacitance, the second capacitor C 2 , C 2 Similarly have equal capacitance.

[0097] In other embodiments of the present invention, the scaling factor S (or α) may be controlled to vary between (close to) -1 and +1 to provide a further increased frequency tuning range. Fig. 9 is a schematic diagram showing a transformer circuit 500 which is identical to the transformer circuit 400 except that the first capacitive voltage divider 442 and the second capacitive voltage divider 444 are connected in an alternative configuration to obtain a scaling factor S (or α) of (close to) -1 to +1.

[0098] In particular, the difference between the transformer circuit 500 and the transformer circuit 400 is that, for the first capacitive voltage divider 442, the second capacitor C 2 connected between the first intermediate node 450 and the second primary terminal, and for the second capacitive voltage divider 444, the second capacitor C 2 is connected between the second intermediate node 452 and the first primary terminal. In other respects, the transformer circuit 500 is identical to the transformer circuit 400 and a repeated description may be omitted.

[0099] Consider again the range of capacitance values ​​between the minimum value (ideally, zero capacitance) and the maximum value (ideally, infinite capacitance), the minimum value can approximate an open circuit connection and the maximum value can approximate a short circuit connection. With this in mind, and referring to Fig. 9 , by forming the first capacitor C of the first capacitive voltage divider 442 1 and the first capacitor C of the second capacitive voltage divider 444 1 Both are set to their maximum values, and the second capacitor C of the first capacitive voltage divider 442 is 2 and the second capacitor C of the second capacitive voltage divider 444 2 Both are set to their minimum values, most of the primary voltage signal V1 (ie, the primary voltage signal V1 minus the first capacitor C 1 , C 1 The voltage drop between the two terminals is applied across the secondary coil, which corresponds to an S (or α) value of (close to) +1. 2 and the second capacitor C of the second capacitive voltage divider 444 2 The first capacitor C of the first capacitive voltage divider 442 is set to their maximum values ​​and 1and the first capacitor C of the second capacitive voltage divider 444 1 Both are set to their minimum values ​​to obtain an S (or α) value (close to) -1. Because in this way, most of the primary voltage signal V1 (i.e., the primary voltage signal V1 minus the first capacitor C 2 , C 2 The voltage drop between ) is applied across the secondary coil, but with opposite polarity.

[0100] It should be understood that the scale factor S (or α) can be controlled to any value between (close to) -1 and +1 depending on the resolution of the capacitance value. Advantageously, by providing a scale factor S (or α) that can be controlled within the range of (close to) -1 to +1, the frequency tuning range for the transformer circuit 500 is further increased compared to the transformer circuit 400.

[0101] use Figure 8 and Fig. 9 The capacitor in the Figure 7 The amplifier in provides additional advantages. In particular, the additional current required to operate the amplifier is not necessary to control the capacitor, and thus transformer circuits 400 and 500 consume less power and are more efficient than transformer circuit 300. In addition, the amplifier includes active components such as transistors (e.g., BJTs or FETs such as MOSFETs), which introduce additional noise into transformer circuit 300 compared to transformer circuits 400 and 500. By replacing transistors with capacitors, transformer circuits 400 and 500 provide improved noise performance.

[0102] As discussed above, the primary coil drivers of transformer circuits 100 , 200 , 300 , 400 , and 500 may be configured such that the entire transformer circuit constitutes an amplifier or an oscillator. Fig.10 is a schematic diagram showing a transformer circuit 600, wherein the primary coil driver is a relevant portion 610 of a transconductance amplifier, so that the transformer circuit 600 as a whole constitutes a transconductance amplifier. Similarly, Fig.11 is a schematic diagram showing a transformer circuit 700 in which the primary coil driver is a relevant portion 710 of a voltage controlled oscillator (VCO), such that the transformer circuit 700 as a whole constitutes a VCO.

[0103] Fig.12 is a schematic diagram showing a circuit 800 constituting a detailed example of a VCO, wherein: Figure 8 The transformer circuit 400 is used to tune the resonant frequency or operating frequency (and thus the frequency of the VCO output signal). Element 810 of the VCO 800 including elements 812 , 814 , and 816 may be considered to correspond together to a primary coil driver for the transformer circuit 400 .

[0104] VCO 800 includes current source 812, negative gm cross-coupled NMOS transistor 814, and tuning varactor 816. As indicated, tuning varactor 816 may be referred to as a PLL (Phase Locked Loop) varactor, where VCO 800 is intended, for example, to be used as a VCO of a PLL.

[0105] The cross-coupled NMOS transistors 814 may alternatively be implemented using PMOS transistors or a mix of PMOS and NMOS transistors, as is known to those skilled in the art in other VCO circuit topologies. The VCO current bias may be top biased or tail biased. Additionally, the current source 812 may be replaced by a resistor or removed entirely from the VCO 800. An LC noise filter, additional capacitor banks, and / or additional varactor diodes may be included in the VCO 800 to reduce circuit noise. The transformer circuit 400 is described above with respect to FIG. Figure 8 The VCO operates as discussed to generate a variable inductance between the first primary terminal and the second primary terminal so that the frequency of the VCO output signal can be controlled.

[0106] It should be understood that any of the transformer circuits 100, 200, 300, 400 and 500 embodying the present invention may be provided as part of a VCO, for example as part of a mixed signal circuit such as a DAC or ADC circuit.

[0107] It should be understood that any of the transformer circuits 100, 200, 300, 400, 500, 600 and 700 embodying the present invention may be implemented as an integrated circuit, for example, on an IC chip such as a flip chip. The present invention extends to integrated circuits and IC chips as mentioned above, circuit boards including such IC chips, and communication networks (e.g., Internet fiber optic networks and wireless networks) including such circuit boards, and network devices of such networks. In particular, Fig.13 An amplifier circuit 900 is shown implemented as an integrated circuit 900. The amplifier circuit 900 includes the relevant portion 610 of a transconductance amplifier that is a primary coil driver for any of the transformers 100, 200, 300, 400 or 500, such that the entire circuit 900 is a transconductance amplifier. Fig.14 The PLL circuit 1000 is shown implemented as an integrated circuit 1000. The PLL circuit 1000 includes a circuit 710, 810 as a primary coil driver of any of the transformer circuits 100, 200, 300, 400, and 500. Fig.15 An ADC or DAC circuit 1100 implemented as an integrated circuit 1100 is shown. The ADC or DAC circuit 1100 includes Fig.14 PLL circuit 1000.

[0108] The invention can be implemented in many different ways in light of the above disclosure within the spirit and scope of the appended claims.

Claims

1. A transformer circuit, comprising: a transformer having a primary coil and a secondary coil, the primary coil having a first primary terminal and a second primary terminal, and the secondary coil having a first secondary terminal and a second secondary terminal; as well as a secondary coil driver configured to drive a secondary voltage signal V2 between the secondary terminals, the secondary voltage signal V2 having a target relationship with a primary voltage signal V1 between the primary terminals driven by the primary coil driver, such that an inductance value measured between the primary terminals is controlled by the target relationship, in: The secondary coil driver is implemented as the primary coil driver and a capacitor network connected between the primary coil and the secondary coil, the capacitor network being configured to apply a scaled version of the primary voltage signal V1 to the secondary coil as the secondary voltage signal such that the target relationship is V2∝V1×S, where S is a scaling factor, the capacitor network comprising a first capacitive voltage divider and a second capacitive voltage divider, the first capacitive voltage divider being connected such that a voltage signal applied at the first secondary terminal depends on a voltage signal applied at the first primary terminal, and the second capacitive voltage divider being connected such that a voltage signal applied at the second secondary terminal depends on a voltage signal applied at the second primary terminal, Each of the capacitive voltage dividers comprises a first capacitor and a second capacitor connected in series, such that the first capacitor of each capacitive voltage divider is connected between a first node and an intermediate node of the capacitive voltage divider, and the second capacitor of each capacitive voltage divider is connected between the intermediate node and a second node of the capacitive voltage divider; For the first capacitive voltage divider, the first node is connected to the first primary terminal and the intermediate node is connected to the first secondary terminal; and For the second capacitive voltage divider, the first node is connected to the second primary terminal and the intermediate node is connected to the second secondary terminal, For the first capacitive voltage divider, the second node is connected to the second primary terminal; and For the second capacitive voltage divider, the second node is connected to the first primary terminal.

2. The transformer circuit according to claim 1, wherein: The secondary coil driver is configured to control the driven secondary voltage signal V2 based on the primary voltage signal V1 to maintain the target relationship.

3. The transformer circuit according to claim 1 or 2, wherein: The capacitor network includes a programmable capacitor, and wherein the secondary coil driver is configured to control the scaling factor S based on a control voltage applied to the programmable capacitor to control the target relationship.

4. The transformer circuit according to claim 1 or 2, wherein: For at least one of the capacitive voltage dividers, at least one of the capacitors is a variable capacitor, and wherein the secondary coil driver is configured to control a capacitance value of at least one of the variable capacitors based on a control signal to control the target relationship; and / or For at least one of the capacitive voltage dividers, at least one of the capacitors is a varactor diode, and wherein the secondary coil driver is configured to control a tuning voltage applied to the secondary coil based on a control signal to control the target relationship.

5. An amplifier circuit or an oscillator circuit comprising the transformer circuit according to any one of claims 1 to 4.

6. An integrated circuit comprising the transformer circuit according to any one of claims 1 to 4 or the amplifier circuit or the oscillator circuit according to claim 5.

7. The integrated circuit according to claim 6, wherein: The integrated circuit is an IC chip.

Images