Methods and apparatus for reliably determining subthreshold current densities in transconducting cells

A transconducting circuit, including:

• a master cell configured to assert a regulated bias voltage in response to an unregulated supply voltage, wherein the bias voltage has a lower magnitude relative to ground than does the supply voltage;
• and
• a transconducting slave cell coupled to receive the bias voltage and configured to operate in subthreshold in response to said bias voltage, wherein the master cell includes a current source, a PMOS transistor having a gate at a first node and a drain coupled to the first node, and an NMOS transistor having an NMOS transistor gate coupled to the first node and an NMOS transistor drain coupled to the first node, wherein the PMOS transistor has a source coupled to the current source at a second node, and the bias voltage is the potential at the second node.

A transconducting circuit, including:

• at least one transconducting slave cell coupled to receive a regulated bias voltage and configured to operate in subthreshold in response to said regulated bias voltage;
• and
• a master cell coupled to the at least one transconducting slave cell so as to assert the regulated bias voltage to said at least one transconducting slave cell, wherein the master cell is configured to generate the regulated bias voltage in response to an unregulated supply voltage such that the regulated bias voltage has a lower magnitude relative to ground than does the supply voltage, and wherein the master cell includes regulator circuitry configured to provide precise regulation of the regulated bias voltage over a wide range of load current drawn from the master cell by said at least one transconducting slave cell.

A transconducting circuit, including:

• a master cell configured to assert a regulated bias voltage in response to an unregulated supply voltage, wherein the bias voltage has a lower magnitude relative to ground than does the supply voltage;
• and
• a transconducting slave cell coupled to receive the bias voltage and configured to operate in subthreshold in response to said bias voltage, wherein the slave cell includes multiple stages connected in series, each of the stages comprising a transconducting circuit including at least one transistor coupled to receive the bias voltage and biased in subthreshold by said bias voltage.

A method for programming a subthreshold current density in a transconducting slave cell, including the steps of:

• regulating an unregulated supply voltage to maintain a constant current density in at least one transistor, thereby generating a regulated bias voltage such that said bias voltage has a lower magnitude relative to ground than does the supply voltage and such that said bias voltage remains substantially fixed despite supply voltage variations;
• and
• replicating the constant current density in the transconducting slave cell, including by biasing said transconducting slave cell using the bias voltage, thereby causing said transconducting slave cell to operate in subthreshold despite process and environmental variations including variations in the supply voltage.