Bombaywalla, fig. 2 shows exactly how it can be done. For
any input voltage corresponding duty cycle is created.
Feedback would only improve performance. Modulator itself
might be not 100% linear but most likely linearity error is
created by the Mosfet switches. Their positive and negative
slew rates are different and vary a bit with the load
(creating timing errors). Negative feedback improves timing
but also lowers output impedance increased by the presence
of common mode choke. Early D class amps (tripath) had this
choke outside of the feedback and had loading problems with
many speakers. Icepower uses two different feedbacks. One
is from the output of modulator (improving timing), the
other from the speaker output. At least that's what I
remember from Karsten Nielsen doctorate.
Icepower uses single supply. Speaker (thru Zobel network)
is placed in the bridge made of 4 N-channel Mosfets. Bridge
is connected to GND and +Vs. At any given moment speaker is
always connected between +Vs and GND only direction changes.
Mosfets are turned on in pairs diagonally. At 50% duty
cycle average, filtered voltage on the speaker is zero. Half
of supply voltage is always present on the speaker's
terminals and the output cannot be bridged. Hypex used only
two Mosfets switching speaker between GND and +Vs or -Vs.
This allows output to be bridged.
As for the phase shift - 20 deg is a substantial phase shift
but I have no idea how much it (summing of harmonics) is
audible. Obviously Jeff Rowland wants no phase shift,
extending bandwidth to 350kHz.
I've read few times people saying "I know that class D
requires a lot of negative feedback" Now I hear that it
cannot even operate without feedback. How do they know
that??? If anything, class D requires less feedback since
voltage-duty cycle conversion seems to be more linear than
nonlinear bipolar transistors in class AB output stage.
SACD is an example of class D without any feedback.
Incoming 2.8MHz train of pulses is averaged and becomes a
sound.
any input voltage corresponding duty cycle is created.
Feedback would only improve performance. Modulator itself
might be not 100% linear but most likely linearity error is
created by the Mosfet switches. Their positive and negative
slew rates are different and vary a bit with the load
(creating timing errors). Negative feedback improves timing
but also lowers output impedance increased by the presence
of common mode choke. Early D class amps (tripath) had this
choke outside of the feedback and had loading problems with
many speakers. Icepower uses two different feedbacks. One
is from the output of modulator (improving timing), the
other from the speaker output. At least that's what I
remember from Karsten Nielsen doctorate.
Icepower uses single supply. Speaker (thru Zobel network)
is placed in the bridge made of 4 N-channel Mosfets. Bridge
is connected to GND and +Vs. At any given moment speaker is
always connected between +Vs and GND only direction changes.
Mosfets are turned on in pairs diagonally. At 50% duty
cycle average, filtered voltage on the speaker is zero. Half
of supply voltage is always present on the speaker's
terminals and the output cannot be bridged. Hypex used only
two Mosfets switching speaker between GND and +Vs or -Vs.
This allows output to be bridged.
As for the phase shift - 20 deg is a substantial phase shift
but I have no idea how much it (summing of harmonics) is
audible. Obviously Jeff Rowland wants no phase shift,
extending bandwidth to 350kHz.
I've read few times people saying "I know that class D
requires a lot of negative feedback" Now I hear that it
cannot even operate without feedback. How do they know
that??? If anything, class D requires less feedback since
voltage-duty cycle conversion seems to be more linear than
nonlinear bipolar transistors in class AB output stage.
SACD is an example of class D without any feedback.
Incoming 2.8MHz train of pulses is averaged and becomes a
sound.