Pulse code modulation feedback encoders

Claim 2

A pulse code modulation feedback encoder including an encoding logic circuit to which timing signals may be applied; generator means for generating a feedback voltage dependent upon signals in said logic circuit; two comparators, said feedback voltage being applied to one input of each comparator, means for applying an analogue signal to be encoded to the other input of one comparator, amplifying means for amplifying said analogue signal by a predetermined fixed amount and means for applying said amplified analogue signal to the other input of the other comparator; and gating means for passing the output of said one comparator to said logic circuit to be used in the encoding operation if the analogue signal is above a predetermined level and for passing the output of said other comparator to said logic circuit to be used in the encoding operation if the analogue signal is below said predetermined level.

Claim 3

An encoder as claimed in claim 1 wherein said gating means includes two AND gates and the output from each comparator is fed through a respective one of said two AND gates to said logic circuit, one or other of the two gates being enabled in dependence upon enabling signals fed to the gates from said logic circuit.

Claim 4

An encoder as claimed in claim 2 wherein the logic circuit is arranged to enable the AND gate in the output from said other comparator at the start of each encoding operation so that said output is used in determining the polarity of the analogue signal.

Claim 5

An encoder as claimed in claim 3 wherein the aforesaid predetermine level is the voltage represented by the first amplitude digit of the P.C.M. code and said logic circuit enables the AND gate in the output from said one comparator immediately after the polarity detection and inhibits the other AND gate, and the comparator is then used to detect whether the analogue input is above or below said predetermined level and if the former applies the enabled AND gate is left enabled and if the latter applies the enabled AND gate is inhibited and said other AND gate is enabled for the remainder of the encoding operation.

Claim 6

A pulse code modulation feedback encoder comprising, in combination: first and second comparators each having a pair of input terminals and an output terminal; means for applying a first input signal to one input terminal of said first comparator and a second input signal to one input terminal of said second comparator in which said first and second input signals are different fixed multiples of an analogue signal to be encoded; means for applying a reference signal to the other input terminals of said first and second comparators; gate means for passing only the output signal at the output terminal of one of said first and second comparators; and means controlling said gate means for passing the signal from said first comparator when an analogue signal to be encoded exceeds a predetermined value established by said reference signal and for passing the signal from said second comparator when an analogue signal to be encoded is less than said predetermined value.

Claim 7

A pulse code modulation feedback encoder comprising, in combination: first and second comparators each having a pair of input terminals and an output terminal; means for applying a first input signal to one input terminal of said first comparator and a second input signal to one input terminal of said second comparator in which said first and second input signals are different fixed multiples of an analogue signal to be encoded; means for applying a reference signal to the other input terminals of said first and second comparators; gate means for passing only the output signal at the output terminal of one of said first and second comparators; and means controlling said gate means for passing the signal from said first comparator when an analogue signal to be encoded exceeds a predetermined value established by said reference signal and for passing the signal from said second comparator when an analogue signal to be encoded is less than said predetermined value.

Claim 8

A pulse code modulation feedback encoder as defined in claim 5 wherein the last mentioned means comprises encoder means for producing a digital output corresponding to an analogue signal to be encoded; said means for applying produces reference signals corresponding to said digital output and includes means for producing a reference signal of fixed amplitude at the beginning of a cycle whereby to select the comparator utilized during the ensuing portion of the cycle.