AN OSCILLATOR DEVICE COMPRISING AN ACTIVE CIRCUIT DEVICE, A CIRCUIT BOARD, AND A RESONATOR CAVITY

TECHNICAL FIELD

The present disclosure relates to an oscillator device comprising at least one active circuit device with an amplifier unit, where the oscillator device further comprises a cavity resonator.

BACKGROUND

Microwave backhaul links are demanding higher capacity in future networks, and require new frequencies at higher bands with more continuous spectrum available, or increasing capacity for lower frequency bands. Oscillators are used for delivering a signal with a predetermined frequency, which may be adjustable. However, all oscillators that are set to a certain frequency tend to vary slightly around said frequency. This variation is known as phase noise.

In order to achieve low phase noise in an oscillator, it is well known that one of the main contributing parameters is the losses of the resonator, measured by its so-called Q factor, where a high Q means low losses and low phase noise. Especially for a Voltage Controlled Oscillator (VCO) where an electrical tuning element is coupled to the resonator, it is very difficult to acquire a low phase noise.

The frequency generation for a radio link normally involves a phase or frequency locked synthesizer (PLL) at some frequency. Dependent on the final frequency or used technology, this frequency can be a subharmonic of the final frequency, which means that frequency multiplicators are used in the distribution network. Normally, the RF-front-end with an up-converting or downconverting mixer itself contains a frequency multiplication of the LOs, to avoid distributing too high frequency on board, and keep the highest LO-frequency inside the RF-circuitry or system-in- package (SIP) module.

The subharmonic or fundamental LO synthesizer can be centrally placed on a radio board and be optimized in frequency to achieve best phase noise (PN) performance but will also have demands on PN-performance to have budget for the degradation in PN due to multiplication afterwards. Also, these synthesizers can be shared between radio parts in a multi-stream e.g., in a line-of-sight (LOS) MIMO system, and be shared, or at least, locked to same common reference for both transmitter and receiver paths.

Overall, the requirement on the fundamental synthesizer frequency generator will have a high phase-noise requirement in the system but on the same time if they can be shared between paths in multi-stream radio, or between receiver and transmitter, they are permitted to slightly increase in size and can be placed in a shield with better vibration, temperature, or more robust environment etc. Alternative solutions for good oscillators are yttrium iron garnet oscillator (YIGs) or dielectric resonator oscillator (DROs), which are both bulky and expensive.

Also, the frequency tuning for channel raster is set by the fundamental frequency generator, the high tunability and low phase noise with a high-quality factor resonator is often contradictory. Especially if external resonators as for DRO:s or cavity oscillators is used, the tuning elements (varactors) and the active amplifier to feed the resonator will come apart from the resonator itself making the in-phase length between amplifier and resonator sensitive to phase difference when tuning frequencies. Bond wires and packaging with undesired parasitic are commonly used for the active devices to their external resonators, and this will all limit the tuning range.

There exist a vast number of different technologies for realizing an oscillator. Basically, an oscillator is formed by an amplifier that is coupled to a resonator, where the resonator normally incorporates the tuning element. Often cavity oscillators are preferred, where a tuning mechanism can be placed inside the cavity.

Furthermore, the coupling structure to the resonator for RF-excitation often entails a distance to the active device which is critical for the phase condition. This distance can limit the tuning bandwidth to fulfil the phase condition for optimal oscillation. The coupling impedance to the resonator is also critical, and sensitive for variations. The remedy is to use a minimum number of physical interfaces and a higher integration. Furthermore, tunability of the cavity are often today made by quite complex and bulky arrangements, e.g. by screws, trombones for phase adjusting,

One example of a cavity oscillator with decreased distances is disclosed in WO 2021/121551 Al, but it is still desired to provide an enhanced oscillator device that comprises a cavity resonator with increased Q-values and decreased phase noise for the desired frequency bands.

There is thus a need for an enhanced oscillator device that comprises a cavity resonator, such as a metal cavity resonator or metalized cavity resonator, where the above drawbacks are alleviated.

SUMMARY

The object of the present disclosure is to provide an enhanced oscillator device that comprises an active circuit device with an amplifier unit, where the oscillator device further comprises a cavity resonator. There should be an increased Q-value and decreased phase noise for the desired frequency bands compared to previously known oscillator devices. This object is achieved by means of an oscillator device comprising at least one active circuit device, a circuit board and a resonator cavity that comprises a resonator cavity cover and electrically conducting inner walls. The circuit board comprises a first main side and a second main side, where each active circuit device comprises an active layer and a circuit die. Each active circuit device is mounted to the first main side such that the active layer is positioned on a side of the circuit die that faces the circuit board. The resonator cavity cover is also positioned on the first main side, enclosing the active circuit device. At least one active circuit device further comprises at least one excitation via connection that runs through the circuit die and electrically connects the active layer to an excitation structure positioned on a side of the circuit die that faces away from the circuit board.

This means that a high-Q oscillator device is provided that is excited with a minimum in-phase length to an active device for oscillation. This also means that the tuning bandwidth will be increased, and the feedback loop will have minimum loss. Frequency tuning can be performed efficiently by direct coupling to the field inside the resonator cavity with maintained high Q value.

Since the active layer with active circuitry and the excitation structure are integrated on the same active circuit device inside the resonator cavity, the yield will be increased due to a smaller number of interfaces between the resonator cavity and the active circuit device, resulting in lower assembly cost.

According to some aspects, the resonator cavity is adapted to enclose two or more separate active circuit devices with separate circuit dies.

This enables combination of different chip technologies for amplifier, varactor tuning, MEMS- switching functions blocks etc. Also, separated circuit dies may be needed to place functions apart for most efficient connection to the fields, or isolate functions for amplifier for feeding or buffer for coupling out power etc.

According to some aspects, the circuit board comprises a first main side metallization, a second main side metallization, and at least one dielectric layer positioned between the first main side metallization and the second main side metallization.

This means that the circuit board can be of a standard type.

According to some aspects, each active circuit device is electrically connected to mounting pads comprised in the first main side metallization. This enables an uncomplicated and reliable connection between the active circuit device and the circuit board.

According to some aspects, a closing wall comprised in the first main side metallization on the first main side, and the resonator cavity cover, together form the resonator cavity, where the resonator cavity cover comprises an opening that is facing the closing wall.

This means that the resonator cavity can be formed in an uncomplicated manner.

According to some aspects, the circuit board is a multi-layer circuit board that comprises at least one intermediate metallization layer comprising at least one of a ground plane, signal connections and power supply connections.

This means that the circuit board can comprise several signal layers and ground layers, which provides a high degree of versatility.

There are also disclosed herein methods associated with the above-mentioned advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described more in detail with reference to the appended drawings, where:

Figure 1 schematically shows a perspective side view of an oscillator device according to the present disclosure;

Figure 2 schematically shows a section side view of the oscillator device according to Figure 1;

Figure 3 schematically shows a section top view of the oscillator device according to Figure 1 and Figure 2;

Figure 4 schematically shows a simplified circuit layout for the oscillator device according to the present disclosure;

Figure 5 shows a flowchart of methods according to embodiments; and

Figure 6 corresponds to Figure 3, showing an example with two active circuit devices. DETAILED DESCRIPTION

Aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings. The different devices, systems, computer programs and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

The terminology used herein is for describing aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

With reference to Figure 1 that shows a side perspective view of an oscillator device 1, Figure 2 that shows a section side view of Figure 1 and Figure 3 that shows a section top view of Figure 2, there is an oscillator device 1 comprising at least one active circuit device 2, a circuit board 3 and a resonator cavity 4 that comprises a resonator cavity cover 21 and electrically conducting inner walls 10a, 10b, 10c, lOd, lOe, lOf.

The circuit board 3 comprises a first main side 6 and a second main side 7, where each active circuit device 2 comprises an active layer 29 and a circuit die 52 and is mounted to the first main side 6 such that the active layer 29 is positioned on a side of the circuit die 52 that faces the circuit board 3. According to the present disclosure, the resonator cavity cover 21 is also positioned on the first main side 6, enclosing the active circuit device 2. At least one active circuit device 2 further comprises at least one excitation via connection 31 that runs through the circuit die 52 and electrically connects the active layer 29 to an excitation structure 9 positioned on a side of the circuit die 52 that faces away from the circuit board 3.

This means that a high-Q oscillator device 1 is provided that is excited with a minimum in-phase length to an active device for oscillation. This also means that the tuning bandwidth will be increased, and the feedback loop will have minimum loss. Frequency tuning can be performed efficiently by direct coupling to the field inside the resonator cavity 4 with maintained high Q value.

Since the active layer 29 with active circuitry and the excitation structure 9 are integrated on the same active circuit device 2 inside the resonator cavity 4, the yield will be increased due to a smaller number of interfaces between the resonator cavity 4 and the active circuit device 2, resulting in lower assembly cost. This will also directly affect the field, compared to DROs (Dielectric Resonator Oscillators) where the coupling needs to be from outside the resonator cavity 4

The circuit die 52 has a certain thickness t as shown in Figure 2, and this will provide an increased coupling as the excitation structure 9 is placed in a position with higher E-field density, compared to an excitation structure that lies in the plane of the first main side 6. The coupling for the excitation structure 9 on the circuit die 52 to the field inside the resonator cavity 4 is dependent on the height t of the circuit die 52 since the E-field is stronger towards middle of the resonator cavity 4.

This building practice with a chip-integrated structure will enhance a solution suitable for relatively high frequencies. The resonator cavity 4 can have be down-scaled to a reduced size for higher resonance frequencies, and the circuit die 52 is likely not limiting size, as the excitation structure 9 also is down-scaled by a higher frequency.

This building practice is suitable for any radio link that has sufficient space to accommodate a resonator cavity 4, and if the resonator cavity 4 can be combined inside already standard shielding or cooling mechanics it is will be very cost effective.

The Integration inside cavity will directly affect the field (compared to DROs where the coupling needs to be from outside).

According to some aspects, the active circuit device 2 is made in flip-chip technology that is well- known and will not occupy more space than already available.

According to some aspects, with reference to Figure 6 that corresponds to Figure 3, the resonator cavity 4 is adapted to enclose two or more separate active circuit devices 2A, 2B with separate circuit dies. In this example there is s first active circuit device 2A and a second active circuit device 2B with a corresponding excitation via connection 31 A, 3 IB and excitation structure 9A, 9B. At least one active circuit device 2A, 2B should comprise an excitation structure.

This enables combination of different chip technologies for amplifier, varactor tuning, MEMS- switching functions blocks etc. Also, separated circuit dies may be needed to place functions apart for most efficient connection to the fields, or isolate functions for amplifier for feeding or buffer for coupling out power etc.

According to some aspects, the circuit board 3 comprises a first main side metallization 12, a second main side metallization 18, and at least one dielectric layer 20 positioned between the first main side metallization 12 and the second main side metallization 18. This means that the circuit board 3 can be of a standard type.

According to some aspects, the active circuit device 2 is electrically connected to mounting pads I la comprised in the first main side metallization 12. This enables an uncomplicated and reliable connection between the active circuit device 2 and the circuit board 3.

According to some aspects, a closing wall 10a is comprised in the first main side metallization 12 on the first main side 6, and the resonator cavity cover 21, together form the resonator cavity 4. The resonator cavity cover 21 comprises an opening 23 that is facing the closing wall 10a. This means that the resonator cavity 4 can be formed in an uncomplicated manner.

According to some aspects, the oscillator device 1 comprises at least one ground via connection 8 that runs through the circuit board 3 and electrically connects the active circuit device 2 to the second main side metallization 18 on the second main side 7.

According to some aspects, the circuit board 3 is a multi-layer circuit board that comprises at least one intermediate metallization layer 19 comprising at least one of a ground plane, signal connections and power supply connections. This means that the circuit board 3 can comprise several signal layers and ground layers, which provides a high degree of versatility.

Figure 4 schematically shows an example of a simplified circuit layout for the oscillator device 1 that comprises the active circuit device 2 and the resonator cavity 4. The circuit layout for the oscillator device 1 can of course be devised in many other ways.

The active circuit device 2 comprises a reflection amplifier unit 5 and a buffer amplifier unit 44 that is connected to an output port 45 to output a signal for low pulling sensitiveness. The reflection amplifier unit 5 is further connected to the cavity resonator 4 via a phase shifter 46 to fulfil the in- phase condition to the resonator and a grounded adjustable varactor 48 for fine-tuning the frequency for locking to a PLL (Phase-Locked Loop) (not shown). Optionally, the phase shifter 46 is connected via a coupling transformer 47 for impedance matching and/or for optimizing the coupling factor to the resonator.

The resonator cavity 4 is in this example represented by a series coupling of a resistor 49, an inductor 50 and a capacitor 51, where, for the case of a tunable oscillator device 1, the inductance 50 and the capacitor 51 are indicated as being adjustable. Many other examples are of course conceivable, for example the resonator cavity 4 can behave as a parallel resonator dependent of how the coupling structure is placed. The components of the active circuit device 2 are according to some aspects comprised in the active layer 29.

It should be noted that Figure 4 only illustrates a very simplified example, other realizations and representations are of course possible. For example, other integrated parts on die level can be a added such as a frequency prescaler for simpler connection to a PLL. A PLL and further a multiplier for frequency up-conversion can also be integrated on the die.

By means of the present disclosure, the phase shifter 46 can be adapted for a relatively small phase span due to the short in-phase length. For example, if, for a wavelength span of 14,3mm-16,7mm, the conductor length between the reflection amplifier unit 5 and the resonator cavity is 3mm, the phase shifter 46 needs to be able to tune about ±5,4°. The present disclosure enables much shorter conductor lengths, a circuit die having a thickness t of 300pm results in an equally long conductor length which means that the phase shifter 46 needs to be able to tune about ±0,5°. This means that the phase shifter 46 does not need to be adapted for a large span.

Both the excitation structure 9 and the active circuit device 2 are positioned on the same circuit die 52. By for example using a flip-chip mounting inside the resonator cavity 4 and let the bottom part of the circuit die 52 contain the excitation structure 9, and have the active circuitry comprised in the active layer 29 on the other side of the circuit die 52, a shielded environment is provided for the bare circuit die 52. Backside processing with hot vias that constitute excitation via connections 31 of for example MMICs (Monolithic Microwave Integrated Circuits) is a standard process. The shape of the radiating pattern of the excitation structure 9 can be adapted to cover the whole backside of the circuit die 52, and therefore it will be standard with common circuit dies 52 using ground connection on this side. Thus, even the simplest semiconductor process with backside processing is supported.

This building practice also support multichip mounting inside the resonator cavity 4 to enable usage of different combined technologies, if different chipset are needed for function blocks such as e.g., amplifier, varactor or MEMS-switches, or if they need to be apart each other.

According to some aspects, the excitation structure 9 is in the form of a radiating patch element that for example can be rectangular, oval or polygonal. The excitation structure 9 can be single- ended with the surrounding ground plane as reference, or differential, if two branched probes are used.

According to the present disclosure, an efficient coupling between an active device and a high-Q resonator is provided, enabling very good phase noise performance. The in-phase condition between active circuits in the active layer 29 and the resonator cavity 4 will be fulfilled over wider frequency tuning range compared to existing solutions due to a minimum feeding distance. The building practice is compatible with standard mechanics where the resonator cavity can be integrated in already existing mechanic for shielding and cooling structure. Also, having the active circuits in the active layer 29 and the excitation structure 9 on same circuit die 52 with good process tolerance will minimize the number of components and increase the yield.

Simulations have revealed that the oscillator device 1 according to the present disclosure presents a Q value around 3000, which should be compared to a normal chip resonator of Q-value around 30. According to Leeson’s equation, this improved Q value means that phase noise at an offset frequency can be enhanced by 40dB. Using realistic assumptions, the oscillator device 1 according to the present disclosure could achieve phase noise of about -135dBc/Hz at 100kHz offset frequency for a carrier frequency of 10GHz. This is to be compared with existing integrated chip resonators, which has -113dBc/Hz at 100k offset for 13GHz oscillation frequency which is suitable for E-band (70-80GHz) radios.

With reference to Figure 5, the present disclosure also relates to a method of configuring an oscillator device 1 comprising providing SI a circuit board 3 with a first main side 6 and a second main side 7 and a metallization 12, 18 on each main side 6, 7, providing S2 at least one active circuit device 2 with an active layer 29 and a circuit die 52, and providing S3 a resonator cavity 4 with a resonator cavity cover 21 and electrically conducting inner walls 10a, 10b, 10c, lOd, lOe, lOf.

The method further comprises providing S4 an excitation structure 9 positioned on a side of at least one circuit die 52 that is intended to face away from the circuit board 3, providing S5 at least one excitation via connection 8 that runs through the circuit die 52 and electrically connects the active layer 29, mounting S6 the active circuit device 2 to the first main side 6 such that the active layer 29 is positioned on a side of the circuit die 52 that faces the circuit board 3, and positioning S7 the resonator cavity cover 21 on the first main side 6, enclosing the active circuit device 2.

According to some aspects, the resonator cavity 4 is used for enclosing two or more separate active circuit devices 2A, 2B with separate circuit dies.

According to some aspects, mounting S4 the active circuit device 2 comprises one of:

- soldering S61 mounting connectors 32 used in the active circuit device 2 to mounting pads I la provided in the metallization 12 on the first main side 6; or

- gluing S62 mounting connectors 32 used in the active circuit device 2 to the mounting pads I la provided in the metallization 12 on the first main side 6. According to some aspects, the resonator cavity 4 is formed by the electrically conducting cover 21 having an opening 23, and a closing wall 10a comprised in a metallization 12 on the first main side 6. Positioning S7 the resonator cavity cover 21 on the first main side 6 comprises placing the opening 23 of the cavity resonator cover 21 over the active circuit device 2 and the closing wall 10a.

According to some aspects, the method comprises electrically connecting each active circuit device 2 to mounting pads I la comprised in the first main side metallization 12, the circuit board 3 having a first main side metallization 12, a second main side metallization 18, and at least one dielectric layer 20 positioned between the first main side metallization 12 and the second main side metallization 18.

The present disclosure is not limited to the above, but may vary freely within the scope of the appended claims. For example, the resonator cavity cover 21 comprises electrically conducting inner walls 10b, 10c, lOd, lOe, lOf, and can for example be die-casted in a metal such as aluminum or in metalized plastic.

Tuning of the oscillator device 1 can be achieved in many ways, for example as disclosed in WO 2019242859. Other tuning mechanism in the cavity resonator 4 can be screws, or Microelectromechanical systems (MEMS) switches that are used for changing the electrical size of the cavity resonator 4.

The circuit board 3 can be any type of PCB (Printed Circuit Board) and can according to some aspects comprise any suitable dielectric carrier materials in one or more layers and corresponding metallization layers.