Distributed class G type amplifier switching method
View Patent ↗An improved Class G type amplifier which switches between multiple power rails depending upon the instantaneous amplitude of the input signal versus the power rails. The low voltage (inner) amplifier includes a plurality of parallel amplifier devices, and the high voltage (outer) amplifier includes a plurality of parallel amplifier devices. A plurality of switches each couples the input signal to either a respective one of the inner amplifier devices or a respective one of the outer amplifier devices. The switches are activated sequentially, such that the switching from inner to outer amplifier devices or vice versa is staggered over some period of time. This avoids having a single, large glitch in the output, and spreads multiple smaller glitches over enough time that some of the glitch energy can fall within the frequency range where the amplifier's feedback circuitry can eliminate its noise. The switches are sequentially activated by a series of delay elements.
1. An amplifier comprising:
(A1) a comparator;
(B1) a first amplifier section including,
a first switch coupled to be controlled by an output of the comparator,
a first inner amplifier device coupled to a first output of the first switch, and
a first outer amplifier device coupled to a second output of the first switch; and
(C1) at least one second amplifier section each including,
a delay element coupled to receive a comparator result from an immediately previous amplifier section,
a second switch coupled to be controlled by a delayed output of the delay element,
a second inner amplifier device coupled to a first output of the second switch, and
a second outer amplifier device coupled to a second output of the second switch;
wherein inputs of the amplifier devices are coupled in parallel to receive an input signal and outputs of the amplifier devices are coupled in parallel to provide an amplified output signal.
2. The amplifier of claim 1 wherein elements A1, B1, and C1 together comprise a positive side of the amplifier, and the amplifier further comprises corresponding elements A2, B2, and C2 which together comprise a negative side of the amplifier.
3. The amplifier of claim 1 wherein there are at least two of the second amplifier sections.
4. The amplifier of claim 1 wherein:
the first inner amplifier device comprises a first current mirror;
the first outer amplifier device comprises a second current mirror;
the second inner amplifier device comprises a third current mirror;
the second outer amplifier device comprises a fourth current mirror.
5. An amplifier stage comprising:
an input node for receiving an input signal;
an output node for providing an amplified output signal;
an outer power rail;
an inner power rail;
a plurality of amplifier devices each having,
an input coupled to the input node,
an output coupled to the output node; and
a control mechanism coupled to the amplifier devices to selectively, individually control whether each is coupled to the outer power rail or the inner power rail,
wherein the control mechanism comprises:
a plurality of switches each coupled to a respective one of the amplifier devices;
a delay chain having an input coupled to receive a signal initiating a shift of the amplifier stage from one to the other of the outer power rail and the inner power rail, and including a series of delay elements each coupled to a respective one of the switches.
6. A method of amplifying an input signal to produce an output signal, the method comprising:
receiving the input signal at a plurality of switches, wherein each switch is coupled to selectably provide the input signal to either a respective inner amplifier device or a respective outer amplifier device associated with the switch, depending upon a control signal received by the switch;
comparing the output signal to an inner voltage reference signal which supplies the inner amplifier devices, and, responsive to the comparing,
if a voltage of the output signal becomes great enough that the inner voltage reference signal is inadequate to provide proper amplification by the inner amplifier devices, sequentially causing the plurality of switches to provide the input signal to their respective associated outer amplifier devices, and
if the voltage of the output signal becomes small enough that the inner voltage reference signal is adequate to provide proper amplification by the inner amplifier devices, sequentially causing the plurality of switches to provide the input signal to their respective associated inner amplifier devices,
wherein the sequential causing is performed by:
passing a result of the comparing through a series of delay elements, each delay element being coupled to provide its delayed output to a control input of a respective associated one of the switches;
whereby the series of delay elements staggers switching of the plurality of switches and thereby spreads switching glitches over a period of time.
7. The method of claim 6 further comprising:
performing the receiving, comparing, and alternative sequentially causing steps in both a positive side and a negative side of an amplifier.