Split cascode circuits and related communication receiver architectures

An apparatus comprising:

• an input to receive an input signal;
• a first controllable switch coupled to a first voltage supply rail and having a first control terminal;
• a second controllable switch coupled to a second voltage supply rail and having a second control terminal coupled to the first control terminal, the second voltage supply rail being different from the first voltage supply rail;
• a split cascode structure comprising multiple cascode circuit paths coupled between the first controllable switch and the second controllable switch, each of the cascode circuit paths comprising a respective pair of controllable switches;
• a feedback path coupled to the first and second control terminals and to a feedback point between the pair of controllable switches of one of the cascode circuit paths;
• and
• a gain controller, the gain controller comprising
• a split cascode stage comprising:
• a third controllable switch coupled to the first voltage supply rail and having a control terminal;
• a fourth controllable switch coupled to the second voltage supply rail and having a control terminal coupled to the control terminal of the third controllable switch;
• multiple cascode circuit paths coupled between the third controllable switch and the fourth controllable switch, each of the multiple cascode circuit paths of the split cascode stage comprising a pair of controllable switches;
• respective resistors coupling together the control terminals of the controllable switches of the cascode circuit paths in the split cascode stage that are coupled to the third controllable switch and coupling together the control terminals of the controllable switches of the cascode circuit paths in the split cascode stage that are coupled to the fourth controllable switch;
• and
• feedback paths coupled to the control terminals of the third and fourth controllable switches and to respective feedback points between the pairs of controllable switches of the cascode circuit paths in the split cascode stage;
• and
• a current mirror and amplifier stage comprising:
• a variable current source;
• a current mirror coupled to the variable current source and to a control terminal of a controllable switch, of the pair of controllable switches of one of the cascode circuit paths in the split cascode stage, which is coupled to the fourth controllable switch;
• and
• an amplifier coupled to the current mirror, the amplifier having an output coupled to a control terminal of a controllable switch, of the pair of controllable switches of the one of the cascode circuit paths in the split cascode stage, which is coupled to the third controllable switch, the amplifier further having inputs coupled across one of the feedback paths that is coupled to the control terminals of the third and fourth controllable switches and to one of the respective feedback points between the pairs of controllable switches of the cascode circuit paths in the split cascode stage,
• wherein gain control signals to control the pair of controllable switches of the one of the cascode circuit paths in the split cascode stage are generated at the control terminals of the pair of controllable switches of the one of the cascode circuit paths in the split cascode stage.

An apparatus, comprising:

• an input to receive an input signal;
• a first controllable switch coupled to a first voltage supply rail and having a first control terminal;
• a second controllable switch coupled to a second voltage supply rail and having a second control terminal coupled to the first control terminal, the second voltage supply rail being different from the first voltage supply rail;
• a split cascode structure comprising multiple cascode circuit paths coupled between the first controllable switch and the second controllable switch, each of the cascode circuit paths comprising a respective pair of controllable switches;
• a feedback path coupled to the first and second control terminals and to a feedback point between the pair of controllable switches of one of the cascode circuit paths;
• a third controllable switch coupled to the first voltage supply rail and having a control terminal coupled to a variable load;
• a fourth controllable switch coupled to the second voltage supply rail and having a control terminal coupled to the variable load;
• multiple further cascode circuit paths coupled between the third controllable switch and the fourth controllable switch, each of the further cascode circuit paths comprising a pair of controllable switches;
• feedback paths coupled to the variable load and to respective feedback points between the pairs of controllable switches of the further cascode circuit paths;
• and
• a bias circuit coupled to control terminals of the pair of controllable switches of one of the cascode circuit paths and to the variable load, to generate control signals to control the pair of controllable switches and the variable load,
• wherein a load point between the pair of controllable switches of the one of the cascode circuit paths is coupled to an output point between the pair of controllable switches of one of the cascode circuit paths of the apparatus.

A method comprising:

• receiving an input signal in a split cascode circuit that includes a first controllable switch coupled to a first voltage supply rail and having a first control terminal, a second controllable switch coupled to a second voltage supply rail different from the first voltage supply rail and having a second control terminal coupled to the first control terminal, multiple cascode circuit paths coupled between the first controllable switch and the second controllable switch, each of the cascode circuit paths comprising a respective pair of controllable switches, and a feedback path coupled to the first and second control terminals and one of the cascode circuit paths;
• controlling gain and input impedance of the split cascode circuit by controlling current flow through the multiple cascode circuit paths,
• wherein the receiving comprises receiving the input signal at an input which is coupled to one of the first and second control terminals of the controllable switches or an input point between a pair of controllable switches of the one of the cascode circuit paths,
• wherein controlling current flow comprises controlling the pair of controllable switches in at least one of the cascode circuit paths based on a gain control signal,
• the method further comprising controlling, based on the gain control signal, an output impedance of an input circuit that is coupled to the input in a low pass configuration.