FIELD OF THE INVENTION

Illustrative embodiments of the invention generally relate to transducers and, more particularly, illustrative embodiments of the invention relate to improving the dynamic range of a transducer.

BACKGROUND OF THE INVENTION

A micro-electro-mechanical system (MEMS) acoustic transducer/sensor coverts acoustic energy into electrical signal, and/or converts an electrical signal into acoustic energy. An example of a MEMS acoustic transducer is a MEMS microphone, which converts sound pressure into an electrical voltage. Based on their transduction mechanisms, MEMS microphones can be made in various forms, such as capacitive microphones or piezoelectric microphones.

MEMS capacitive microphones and electret condenser microphones (ECMs) currently dominate the consumer electronics market. Piezoelectric MEMS microphones, however, occupy a growing portion of the consumer market, and have unique advantages compared to their capacitive counterparts. Among other things, piezoelectric MEMS microphones do not have a back plate, eliminating the squeeze film damping, which is an intrinsic noise source for capacitive MEMS microphones. In addition, piezoelectric MEMS microphones are reflow-compatible and can be mounted to a printed circuit board (PCB) using typical lead-free solder processing, which could irreparably damage typical ECMs.

Transducers have standard metrics, such as the well-known acoustic overload point. Meeting these specifications has proven challenging.

SUMMARY OF VARIOUS EMBODIMENTS

In accordance with one embodiment of the invention, a MEMS transducer system has a transducer configured to convert a received signal into an output signal. The transducer further has an output port for forwarding the output signal. The system also has an integrated circuit (“IC”) with an IC input in electric communication with the transducer output port. The IC input is configured to receive an IC input signal produced as a function of the output signal. In addition, the system has an attenuator coupled between the IC input and the transducer output port. The attenuator is selectably actuatable and configured to selectively attenuate one or more signals into the IC input to at least in part produce an attenuated IC input signal. The attenuator may be integral with the integrated circuit or separate from the integrated circuit.

Among other things, the attenuator may include a dividing element, which is selectably actuatable and coupled between the IC input and the transducer output port. The dividing element may include, for example, at least one attenuation branch. Each such attenuation branch preferably has a switch and a capacitance (e.g., one or more capacitors) in series with the switch. More specifically, the dividing element may include a plurality of attenuation branches that each has a switch and a capacitance in series with the switch. The integrated circuit may have a mode pin configured to actuate the at least one attenuation branch when receiving a first signal, and to disable the at least one attenuation branch when receiving a second signal. The system also may have memory configured to store information for selectably actuating prescribed attenuation branches.

Among other things, the transducer may be at least one of a microphone, speaker, accelerometer, tilt sensor (e.g., implemented as a low-G accelerometer) gyroscope, inertial sensor, chemical sensor, pressure sensor, and/or ultrasonic transducer. For example, the transducer may include a MEMS device, such as a MEMS piezoelectric microphone.

The integrated circuit preferably includes an application specific integrated circuit with an operational amplifier having a non-inverting input and an op-amp output. In that case, the IC input may be coupled with the non-inverting input, and have an output coupled with the op-amp output. Moreover, the dividing element may be coupled with a node connecting the IC input and transducer output port and, as such, be electrically in parallel with the transducer output port.

The transducer and integrated circuit of this and other embodiments discussed below each may be part of the same die. Alternatively, the transducer and integrated circuit of this and other embodiments discussed below each may be formed on different dies (e.g., a transducer die and an integrated circuit die).

For some embodiments, the transducer has a plurality of sense members configured to independently move in response to a pressure signal to produce a plurality of member signals. The attenuator is electrically coupled with at least one of the sense members and is configured to selectively electrically couple fewer than all of the member signals with the IC input.

In accordance with another embodiment, a MEMS microphone has a plurality of sense members configured to flex in response to an acoustic signal incident on the sense members. The plurality of the sense members are electrically coupled with a first pad and a second pad. The microphone also has a plurality of nodes between the sense members, and at least one pick-off pad. Each of the pick-off pads is coupled with no more than one of the nodes between the sense members, and is associated with one of the sense members. In addition, each pick-off pad is configured to cooperate with the second pad to produce an output signal representative of an attenuated version of the acoustic signal incident on the plurality of sense members.

The MEMS microphone may also include an integrated circuit configured to switch between receiving signals from the first output pad and the at least one pick-off pad. Moreover, those skilled in the art may select the appropriate number of pick-off pads. For example, the MEMS microphone could have only one pick-off pad, or a plurality of pick-off pads.

If implemented as a piezoelectric MEMS microphone, then its sense members may include piezoelectric sense members. Some embodiments may connect the plurality of sense members in series.

In accordance with other embodiments, a MEMS transducer system has a transducer configured to convert a received signal into a transducer signal, and an integrated circuit in communication with the transducer to receive the transducer signal. The transducer further includes a transducer ground node and, in a similar manner, the integrated circuit may have an IC ground node. The integrated circuit further has an output and is configured to process the received transducer signal to produce an IC output signal, which may be an AC signal, at the output. The transducer ground node illustratively is coupled with the integrated circuit output to receive the IC output signal. Accordingly, in preferred embodiments, the transducer ground node receives an attenuated and inverted version of the IC output signal.

To that end, illustrative embodiments may have a feedback segment electrically connecting the output of the integrated circuit with the transducer ground node. The feedback segment may have an amplifier configured to selectively amplify or attenuate the IC output signal.

