FIELD OF DISCLOSURE

The field of representative embodiments of this disclosure relates to methods, apparatus and/or implementations concerning or relating to operation of driver circuitry, and especially to driver circuitry for driving transducers, such as loudspeakers, and in particular to driving relatively low-impedance transducers arranged as a bridge-tied-load.

BACKGROUND

There are a number of applications where it is desired to drive an output transducer, e.g. a load, with some signal content, for instance to drive a loudspeaker with an audio signal to generate sound. Typically, the audio signal content will be received or stored for playback in digital form and thus a playback path for driving a loudspeaker may include a digital-to-analogue converter (DAC), to convert the digital audio signal to analogue, and a suitable amplifier, to amplify the output of the DAC to generate a driving signal. In some applications, the loudspeaker, or more generally load, is connected in series between a terminal for receiving the driving signal and a terminal held at a fixed voltage, e.g. ground. In some applications, however, the loudspeaker may be arranged in a bridge-tied-load configuration, where the two terminals of the loudspeaker are each driven with a differential driving signal so as to apply a differential voltage across the bridge-tied-load, e.g. loudspeaker. Such a configuration may involve two audio driving paths for the loudspeaker, each involving a DAC and amplifier.

In some applications, size and/or power consumption of the driver circuitry may be important. For example, wireless earbuds or in-ear headphones are becoming popular. The size of such devices is limited by the need to fit and remain comfortable within a user's ear and thus the size of the internal components, such as the driver circuitry, can be important. To provide a good user experience the device should, in use, also offer a decent battery life before requiring charging and thus power consumption is also important, especially given the battery size will also be limited. For headphones or the like, the loudspeaker of the device may have a relatively low impedance, say of the order of 8-1000 ohms, and in some instance, e.g. for in-ear headphones or the like which may be relatively small the impedance may be 16 ohms or 32 ohms or so, and the driver circuitry should be capable of operating stably to drive such a relatively low-impedance load.

SUMMARY

Embodiments of the present disclosure are thus directed at driver circuitry, and operation thereof, suitable for driving a bridge-tied-load, for example a relatively low-impedance transducer such as a loudspeaker, that may offer advantages in terms of size and/or power consumption.

According to an aspect of the disclosure there is provided driver circuitry for receiving a digital input signal and outputting, at first and second output nodes, first and second analogue driving signals respectively for driving a bridge-tied-load. The driver circuitry comprises first and second digital-to-analogue converters configured to receive the digital input signal, wherein outputs of the first and second digital-to-analogue converters are coupled to the first and second output nodes respectively. A differential-output amplifier circuit has outputs connected to the first and second output nodes respectively, wherein the differential-output amplifier circuit is configured to regulate the outputs of first and second digital-to-analogue converters at the first and second output nodes to provide the first and second analogue driving signals.

In some examples the differential-output amplifier circuit may comprise first and second amplifiers with respective outputs coupled to the first and second output nodes respectively. A first input of the first amplifier and first input of the second amplifier may be coupled to a common-input node, the common input node being configured to receive a voltage based on a defined common-mode voltage.

The first and second digital-to-analogue converters may be connected across the respective first and second amplifiers between a second input of the respective first or second DAC amplifier and the output of the respective first or second DAC amplifier.

The common-input node may be coupled to receive the defined common-mode voltage. In some implementations the common input node may be coupled to the defined common-mode voltage via a series resistance.

In some examples, for each of the first and second amplifiers, there may be a feedback impedance in a feedback path from a tap node of a signal path of the relevant amplifier and the first input of the amplifier. The tap node of the signal path may be upstream of an output stage of the amplifier. The feedback impedance may comprise at least one reactive component and, in some examples, may comprise a capacitor.

In some implementations the driver circuitry may comprise a common-mode regulating amplifier having a first input coupled to receive the defined common-mode voltage, a second input coupled to receive an indication of the common-mode voltage at the first and second output nodes and an output coupled to the common input node.

The first and second digital-to-analogue converters may comprise switched capacitor direct-charge-transfer DACs.

The differential-output amplifier circuit may comprise a two-stage amplifier.

In some implementations, the first and second analogue driving signals are for driving a bridge-tied-load transducer with an impedance or 1000 ohms or less, or 650 ohms or less, or 200 ohms or less. In some implementations the first and second analogue driving signals are for driving a bridge-tied-load transducer with an impedance or 64 ohms or less.

The driver circuitry may be implemented as an integrated circuit.

Embodiments also relate to driver circuity further comprising a transducer load coupled in series between the first and second output nodes. The transducer load may be a loudspeaker. The driver circuitry may be configured so that there are no amplification stages in signal paths between the first and second output nodes and the transducer load.

Also provided is an electronic device comprising driver circuitry according to any of the variants discussed herein.

In another aspect there is provided circuitry for driving a transducer comprising:an amplifier comprising differential input terminals and differential output terminals for outputting a differential analogue output signal for driving the transducer; anda switched capacitor DAC arrangement comprising an input terminal for receiving a digital input signal,
wherein the switched capacitor DAC arrangement is operatively connected between the amplifier differential input terminals and the amplifier differential output terminals.

In another aspect there is provided circuitry for driving a transducer comprising: a differential amplifier for outputting a differential analogue output signal for driving the transducer; and a differential DAC connected in parallel with the amplifier.

In another aspect there is provided a differential amplifier for driving a transducer comprising a differential DAC connected in parallel with the differential amplifier.

Unless expressly indicated to the contrary, any of the various features of the various implementations discussed herein may be implemented together with any one or more of the other described features in any and all suitable combinations.

