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US 6,515,540 B1Granted
High order multi-path operational amplifier with output saturation recovery
AssigneeCirrus Logic, Inc.
InventorsAmmisetti V. Prasad, Murari Kejariwal, Axel Thomsen
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Abstract
An amplifier is disclosed including multiple integrator stages. The amplifier includes a low-frequency path from a signal input to a signal output and relatively higher-frequency bypass paths around the first integrator stage. The paths converge at a summing node. To prevent instability when the integrators are saturated by large signals, the circuit includes a saturation detector which disables the relatively low-frequency paths during such saturation conditions.
Claims27
An operational amplifier comprising:
- a) an operational amplifier signal input;
- b) an operational amplifier signal output;
- c) a operational amplifier reference voltage input;
- d) a first amplifier, said first amplifier having an input connected to said operational amplifier signal input and having an output;
- e) a second amplifier having an input connected to said output of said first amplifier and having an output;
- f) a summer, said summer having a first input connected to said output of said second amplifier, a second input, a third input, and an output;
- g) a first bypass signal path around said second amplifier, said first bypass signal path connected at one end to the signal path between said first and second amplifiers and at the other end to said second input of said summer;
- h) a third amplifier having an input connected to said output of said summer and having an output connected to said operational amplifier signal output;
- i) a second bypass signal path around said first and second amplifiers, said bypass signal path connected at one end to the signal path between said operational amplifier signal input and said input of said first amplifier, and at the other end to said third input of said summer;
- j) a saturation detector connected to said third amplifier, said saturation detector operable to detect when said third amplifier is in saturation and to assert an output signal indicating that saturation;
- k) a cut-off switch connected to the signal paths into said first and second inputs to said summer and to a reference voltage provided to said operational amplifier at said reference voltage input, said cut-off switch operable to connect said signal paths into said first and second inputs to said summer to the reference voltage upon receiving a positively-asserted saturation detection signal from said saturation detector.
8 more elements
An operational amplifier comprising:
- a) an operational amplifier signal input;
- b) an operational amplifier signal output;
- c) an operational amplifier reference voltage input;
- d) a first amplifier, said first amplifier having an input connected to said operational amplifier signal input and having an output;
- e) a second amplifier having an input connected to said output of said first amplifier and having an output;
- f) a first summer, said first summer having a first input connected to said output of said second amplifier, a second input, and an output;
- g) a second summer, said second summer having a first input connected to said output of said first summer, a second input, and an output;
- h) a third amplifier having an input connected to said output of said second summer and having an output;
- i) a fourth amplifier having an input connected to the output of said third amplifier and having an output;
- j) a third summer, said third summer having a first input connected to the output of said fourth amplifier and having a second input, a third input, and an output;
- k) a fifth amplifier having an input connected to said output of said third summer and an output connected to said output amplifier signal output;
- l) a first bypass signal path around said second amplifier, said first bypass signal path connected at one end to the signal path between said first and second amplifiers and at the other end to said second input of said first summer;
- m) a second bypass signal path around said fourth amplifier, said second bypass signal path connected at one end to the signal path between said third and fourth amplifiers and at the other end to said second input of said third summer;
- n) a third bypass signal path around said first and second amplifiers, said third bypass signal path connected at one end to the signal path between said operational amplifier signal input and said input to said first amplifier and at the other end to said second input of said second summer;
- o) a fourth bypass signal path around said first, second, third, and fourth amplifiers, said fourth bypass signal path connected at one end to the signal path between the operational amplifier signal input and said input of said first amplifier and connected at the other end to said third input of said third summer;
- p) a saturation detector connected to said fifth amplifier, said saturation detector operable to detect when said fifth amplifier is in saturation and to assert an output signal indicating such saturation;
- q) a cut-off switch connected to the signal paths into said second amplifier, said first summer, said second summer, said fourth amplifier, and said third summer, and to a reference voltage provided to said operational amplifier at said operational amplifier reference voltage input, said cut-off switch operable to connect said signal paths to the reference voltage upon receiving a positively-asserted saturation detection signal from said saturation detector.
14 more elements
A method for operating a conditionally-stable multipath operational amplifier, said method comprising:
- a) providing a first signal path through at least a first and a second amplifiers;
- b) providing a second signal path around said first and second amplifier;
- c) providing a summer to add the signals from said first and second signal paths;
- d) providing a third amplifier to amplify the added signals from the summer,
- e) establishing the gains of the amplifiers and the relative weightings of the signals through the summer such that the system response of the system is unconditionally stable when only the signal through said second signal path is enabled, and such that the system response of the entire system comprising said first and second signal paths, first and second amplifier, said summer, and said third amplifier is conditionally stable, wherein said system is stable for input signal frequencies of less than the system open-loop unity gain frequency and unstable for input signal frequencies of greater than the system open-loop unity gain frequency;
- f) providing a saturation detector to detect when said operational amplifier is saturated;
- g) disabling said first signal path when said operational amplifier is saturated;
- and
- h) re-enabling said first signal path when said saturation condition is removed.
6 more elements
An operational amplifier comprising:
- a) an operational amplifier signal input;
- b) an operational amplifier signal output;
- c) a operational amplifier reference voltage input;
- d) a first amplifier, said first amplifier having an input connected to said operational amplifier signal input and having an output;
- e) a first summer, said first summer having a first input connected to said output of said first amplifier, a second input, and an output;
- f) a first bypass signal path around said first amplifier, said first bypass signal path connected at one end to the input to said first amplifier and at the other end to said second input of said first summer;
- g) an attenuator having an input connected to the output of said first summer and having an output;
- h) a second summer, said second summer having a first input, a second input, and an output, said first input of said second summer being connected to the output of the attenuator;
- i) a second bypass signal path around said first amplifier, said first summer, and said attenuator, said second bypass signal path being connected at one end to the input to said first amplifier and at the other end to said second input of said second summer;
- j) a chopper amplifier having an input connected to the output of said second summer, and having an output;
- k) a third summer having a first input connected to the output of the chopper amplifier and having a second input and an output;
- l) a third bypass signal path around said first amplifier, said chopper amplifier, said attenuator, and said first and second summers, said third bypass signal being connected at one end to said input to said first amplifier and at the other end to said second input of said third summer;
- m) a third amplifier having an input connected to said output of said summer and having an output connected to said operational amplifier signal output;
- n) a saturation detector connected to said third amplifier, said saturation detector operable to detect when said third amplifier is in saturation and to assert an output signal indicating that saturation;
- and
- o) a cut-off switch connected to the signal paths into at least said third summer, said cut-off switch operable to connect said signal path to the reference voltage upon receiving a positively-asserted saturation detection signal from said saturation detector.
13 more elements
An operational amplifier comprising:
- a) an operational amplifier signal input;
- b) an operational amplifier signal output;
- c) a operational amplifier reference voltage input;
- d) a chopper amplifier, said chopper amplifier having an input connected to said operational amplifier signal input and having an output;
- e) a first amplifier having an input connected to said output of said chopper amplifier and having an output;
- f) a first summer, said first summer having a first input connected to said output of said first amplifier, a second input, and an output;
- g) a first bypass signal path around said first amplifier, said first bypass signal path connected at one end to the signal path between said chopper and said first amplifier and at the other end to said second input of said summer;
- h) a second amplifier having an input connected to said output of said summer and a having an output connected to said operational amplifier signal output;
- i) a saturation detector connected to said second amplifier, said saturation detector operable to detect when said second amplifier is in saturation and to assert an output signal indicating that saturation;
- and
- j) a cut-off switch connected to the signal paths into at least one of said first amplifier and said first summer, and to a reference voltage provided to said operational amplifier at said reference voltage input, said cut-off switch operable to connect said signal paths into said first amplifier and said first summer to the reference voltage upon receiving a positively-asserted saturation detection signal from said saturation detector.
8 more elements
Dependencies are inferred from the claim text.