Precision differential level shifter
AssigneeON Semiconductor
InventorsFrancois Laulanet, Cedric Bonaldi
Life of this patent
Estimating the term…
Abstract
A differential level shifter employs a variable current mirror to maintain a reference voltage at one output while the other output follows a differential input. Resistor networks allow postproduction trimming of load resistors and the current mirror, resulting in a precise and accurate output of the differential signal. An active cascode circuit enhances current mirror balance and high frequency operation.
Claims37
A circuit for shifting the reference level of a differential signal while preserving its amplitude, the circuit comprising:
- a negative input terminal;
- a positive input terminal;
- a first load resistor having a first end and a second end, the first end connected to the negative input terminal;
- a second load resistor having a first end and a second end, the first end connected to the positive input terminal;
- a first pass transistor having a first node, a second node and a control node, the first node connected to the second end of the first load resistor to form a negative output terminal, the control node connected to a selected reference voltage signal;
- a current mirror having a first current node, a second current node and a current control node, the first current node connected to the second node of the first pass transistor, the second current node connected to the second end of the second load resistor to form a positive output terminal;
- and
- a first amplifier having a negative input, a positive input and an output, the positive input connected to the negative output terminal, the negative input connected to the selected reference voltage signal, the output connected to the current control node of the current mirror.
A circuit for shifting the reference level of a differential signal while preserving its amplitude, the circuit comprising:
- a negative input terminal;
- a positive input terminal;
- a first load resistor having a first end and a second end, the first end connected to the negative input terminal;
- a second load resistor having a first end and a second end, the first end connected to the positive input terminal,
- wherein at least one of the load resistors comprises a trimmable resistor;
- and
- a trimmable current mirror having a first current node, a second current node and a current control node, the first current node connected to the second end of the first load resistor to form a negative output terminal, the second current node connected to the second end of the second load resistor to form a positive output terminal.
A method for trimming a current mirror of a differential level shifter, the level shifter having a positive input terminal, a negative input terminal, a positive output terminal, a negative output terminal and a trimmable current mirror, the method comprising:
- (a) applying a high test voltage to the negative input terminal and measuring the resulting current, I1N, into the negative input terminal;
- (b) applying a high test voltage to the positive input terminal and measuring the resulting current, I1P, into the positive input terminal;
- (c) applying a low test voltage to the negative input terminal and measuring the resulting current, I2N, into the negative input terminal;
- (d) applying a low test voltage to the positive input terminal and measuring the resulting current, I2P, into the positive input terminal;
- (e) calculating two ratios (I1N/I2N) and (I1P/I2P);
- (f) adjusting the trimmable current mirror;
- and
- (g) repeating steps (a) through (f) until the difference between the two ratios is below a selected threshold value.
A method for trimming a load resistor of a differential level shifter, the level shifter having a positive input terminal, a negative input terminal, a positive output terminal, a negative output terminal and a trimmable load resistor, the method comprising:
- (a) applying a differential test voltage between the positive input terminal and the negative input terminal;
- (b) measuring the voltage between the positive output terminal and the negative output terminal;
- (c) adjusting the trimmable load resistor;
- and
- (d) repeating steps (a) through (c) until the difference between the differential test voltage and the measured voltage is below a selected threshold value.
A method for trimming a differential level shifter, the level shifter having a positive input terminal, a negative input terminal, a positive output terminal, a negative output terminal, a trimmable current mirror, and a trimmable load resistor, the method comprising:
- (a) applying a high test voltage to the negative input terminal and measuring the resulting current, I1N, into the negative input terminal;
- (b) applying a high test voltage to the positive input terminal and measuring the resulting current, I1P, into the positive input terminal;
- (c) applying a low test voltage to the negative input terminal and measuring the resulting current, I2N, into the negative input terminal;
- (d) applying a low test voltage to the positive input terminal and measuring the resulting current, I2P, into the positive input terminal;
- (e) calculating two ratios (I1N/I2N) and (I1P/I2P);
- (f) adjusting the trimmable current mirror based on the two ratios;
- (g) applying a differential test voltage between the positive input terminal and the negative input terminal;
- (h) measuring the voltage between the positive output terminal and the negative output terminal;
- and
- (i) adjusting the trimmable load resistor based on the difference between the applied differential test voltage and the measured voltage.
A method for trimming a differential level shifter, the level shifter having a positive input terminal, a negative input terminal, a positive output terminal, a negative output terminal, a trimmable current mirror and a trimmable load resistor, the method comprising:
- (a) applying test voltages to the input terminals and adjusting the trimmable the current mirror based on the resulting currents;
- and
- (b) applying a differential signal to the input terminals and adjusting the trimmable load resistor based on the resulting differential output voltage.
A trimmable resistor comprising:
- a primary resistor;
- a plurality of secondary resistors;
- and
- a plurality of switches,
- wherein each switch is in series connection with one of the secondary resistors, and
- wherein each series connection of a switch and a secondary resistor is in parallel connection with the primary resistor.
A trimmable resistor string comprising a plurality of trimmable resistors connected in series.
Dependencies are inferred from the claim text.