Telescopic amplifier with improved common mode settling

A telescopic amplifier, comprising:

• a differential input stage for receiving a positive input signal and a complementary input signal comprising a first input transistor having a gate terminal coupled to a positive input terminal, and a second input transistor having a gate terminal coupled to a complementary input terminal, the first input transistor having a drain and the second input transistor having a drain;
• a differential output stage for outputting a positive output signal and a complementary output signal comprising a first output transistor having a source coupled to the drain of the first input transistor and having a first current source coupled to a drain of the first output transistor, and a second output transistor having a source coupled to the drain of the second input transistor and having a second current source coupled to a drain of the second output transistor, and a first output terminal coupled to the drain of the first output transistor, and a second output terminal coupled to the drain of the second output transistor;
• a tail current transistor having a drain coupled to a common source node coupled to a source of each of the first and the second input transistors, and having a source coupled to a ground potential, and having a gate terminal coupled to a tail gate node;
• a common mode feedback circuit having a first feedback input coupled to the first output terminal, and a second feedback input coupled to the second output terminal, and having a common mode reference signal input;
• and having a common mode output;
• and
• a circuit element coupled between the common mode output and the tail gate node, the circuit element being at least one of a source follower transistor and a resistor;
• whereby a non-dominant pole is formed in a common mode feedback open loop gain transfer function of the telescopic amplifier, due to the circuit element.

A pipelined ADC converter, comprising:

• an input terminal for receiving an analog input voltage;
• an N-bit ADC coupled to the input terminal for outputting a quantized digital signal;
• an N-bit DAC coupled to the quantized digital signal and outputting an analog voltage corresponding to the quantized digital signal;
• a sample and hold circuit coupled to sample and hold an analog input voltage received at the input terminal;
• a summer circuit coupled to the sample and hold circuit and to the analog voltage corresponding to the quantized digital signal, outputting a difference voltage that is a residue voltage obtained from subtracting the analog voltage corresponding to the quantized digital signal from the sample and hold analog voltage;
• and
• a telescopic amplifier coupled to the summer circuit to amplify the residue voltage, further comprising:
• a differential input stage for receiving a positive input signal and a complementary input signal comprising a first input transistor having a gate terminal coupled to a positive input terminal, and a second input transistor having a gate terminal coupled to a complementary input terminal, the first input transistor having a drain and the second input transistor having a drain;
• a differential output stage for outputting a positive output signal and a complementary output signal comprising a first output transistor having a source coupled to the drain of the first input transistor and having a first current source coupled to a drain of the first output transistor, and a second output transistor having a source coupled to the drain of the second input transistor and having a second current source coupled to a drain of the second output transistor, and a first output terminal coupled to the drain of the first output transistor, and a second output terminal coupled to the drain of the second output transistor;
• a tail current transistor having a drain coupled to a common source node coupled to a source of each of the first and the second input transistors, and having a source coupled to a ground potential, and having a gate terminal coupled to a tail gate node;
• a common mode feedback circuit having a first feedback input coupled to the first output terminal, and a second feedback input coupled to the second output terminal, and having a common mode reference signal input;
• and having a common mode output;
• and
• a circuit element coupled between the common mode output and the tail gate node, whereby a non-dominant pole is formed in a common mode feedback open loop gain transfer function of the telescopic amplifier, due to the circuit element.