Open loop bandwidth test architecture and method for phase locked loop (PLL)
First Claim
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1. A phase locked loop (PLL) circuit, comprising:
- a test loop filter, comprisinga resistor-capacitor (RC) network coupled to a control node coupled to a voltage controlled oscillator (VCO), anda test leg coupled to the RC network that includes a test resistance, and at least one test controllable impedance path in series with the test resistance that provides a high impedance in a non-test mode and a low impedance in a test mode.
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Abstract
A phase locked loop (PLL) can include a test loop filter (100) that generates a control voltage (VCTRL) for input to a voltage controlled oscillator (VCO). In a test mode, a control voltage can be varied and resulting output frequencies recorded, from which an open loop bandwidth can be determined. A control voltage can be varied by enabling a switch element (104-1) that can provide a current path through load resistance (RL) of test loop filter (100). Current provided to the test loop filter can be varied according to test signals to provide a variable control voltage (VCTRL).
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Citations
20 Claims
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1. A phase locked loop (PLL) circuit, comprising:
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a test loop filter, comprising a resistor-capacitor (RC) network coupled to a control node coupled to a voltage controlled oscillator (VCO), and a test leg coupled to the RC network that includes a test resistance, and at least one test controllable impedance path in series with the test resistance that provides a high impedance in a non-test mode and a low impedance in a test mode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of testing a PLL circuit, comprising the steps of:
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enabling a test leg with a test signal to draw current through a load resistance of a PLL loop filter and generate a control voltage at an input of a voltage controlled oscillator; varying the control voltage; and measuring the output frequency of the PLL for each of the different control voltages. - View Dependent Claims (13, 14, 15, 16, 17)
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18. A phase locked loop (PLL) circuit, comprising:
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a test loop filter that includes a load resistor coupled to a control voltage node and a test leg that provides a current path through the load resistor that is disabled in a non-test mode and enabled in a test mode; and a voltage controlled oscillator coupled to the test loop filter that generates an output signal having a frequency determined, at least in part, on a control voltage generated on the control voltage node. - View Dependent Claims (19, 20)
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Specification