Low power high speed latch for a prescaler divider
First Claim
1. A prescaler circuit comprising:
- a latch comprising;
a first clocked differential pair comprising input terminals coupled to a data input of the latch, a first output terminal coupled to a first output of the latch, and a second output terminal coupled to a second output of the latch;
a second clocked differential pair with a first input terminal coupled to the second output of the latch, a second input terminal coupled to the first output of the latch;
a first output terminal coupled to the first output of the latch, and a second output terminal coupled to the second output of the latch;
a first shunt peaked active load circuit coupled to the first output of the latch;
a second shunt peaked active load circuit connected to the second output of the latch;
a replica bias circuit to control a voltage of the shunt peaked active loads, wherein the replica bias circuit comprises a transistor stack to replicate a voltage drop across the shunt peaked active loads of the latch, wherein the shunt peaked active loads comprise a resistor and a transistor; and
wherein the replica bias circuit is configured to generate a voltage at the resistors that is higher than a supply voltage of the latch; and
a filter network coupled between the replica bias circuit and the resistors.
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Accused Products
Abstract
A high-speed latch is disclosed that can function at high-speed input clocking frequencies. The active loads used within the latch design exhibit an input impedance that is inductive to the rest of the circuit to improve the driving capability of the overall latch in the presence of loading capacitances. The latch circuit, when used in a system or stand alone divider, will consume very low power while reducing the silicon die area. Possible applications include but are not limited to frequency dividing and counting applications. Of particular interest is the use of this high-speed latch in a prescaler divider as a part of a charge pump phase-locked loop design for single chip CMOS multi-band and multi-standard radio frequency transceiver integrated circuits.
44 Citations
31 Claims
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1. A prescaler circuit comprising:
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a latch comprising; a first clocked differential pair comprising input terminals coupled to a data input of the latch, a first output terminal coupled to a first output of the latch, and a second output terminal coupled to a second output of the latch; a second clocked differential pair with a first input terminal coupled to the second output of the latch, a second input terminal coupled to the first output of the latch;
a first output terminal coupled to the first output of the latch, and a second output terminal coupled to the second output of the latch;a first shunt peaked active load circuit coupled to the first output of the latch; a second shunt peaked active load circuit connected to the second output of the latch; a replica bias circuit to control a voltage of the shunt peaked active loads, wherein the replica bias circuit comprises a transistor stack to replicate a voltage drop across the shunt peaked active loads of the latch, wherein the shunt peaked active loads comprise a resistor and a transistor; and
wherein the replica bias circuit is configured to generate a voltage at the resistors that is higher than a supply voltage of the latch; anda filter network coupled between the replica bias circuit and the resistors. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A prescaler circuit comprising:
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a latch with an active load configured for shunt-peaked amplification, wherein the active load comprises shunt-peaking elements configured to have an inductive impedance that at least partially cancel a capacitive load impedance of the latch, the latch further comprising resistors coupled to the shunt-peaking elements; a replica bias circuit configured to control a voltage of the shunt-peaking elements, wherein the replica bias circuit comprises a transistor stack to replicate a voltage drop across the shunt-peaking elements of the latch, and wherein the replica bias circuit is configured to generate a voltage at the resistors that is higher than a supply voltage of the latch; and a filter network coupled between the replica bias circuit and the resistors. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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19. A method to improve a bandwidth of a latch, the method comprising:
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generating an inductive impedance in the latch with inductorless loads in the latch, wherein the inductorless loads comprise resistors and transistors as shunt-peaking elements, and wherein the transistors have a port that appears as the inductive impedance; tuning a frequency of the latch by using the inductive impedance of the inductorless loads to at least partially cancel a capacitive load impedance of the latch; adjusting a timing requirement of the latch with the tuned frequency to provide the improvement of the bandwidth; biasing the inductorless loads with a replica bias circuit voltage comprising a voltage that is higher than a supply voltage of the latch; and filtering the replica bias circuit voltage with a filtering network coupled to the inductorless loads. - View Dependent Claims (20, 21, 22, 23, 24)
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25. A prescaler circuit comprising:
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at least two latches coupled together to form a flip flop circuit such that when a first latch is in a first mode, a second latch is in an opposite mode, wherein the first mode is either a sample mode or a hold mode; a pair of transistors in at least one of the latches to form a shunt-peaked load in the latch, the pair of transistors being configured to form an inductive impedance to partially cancel a capacitive load impedance of the latch; a bias circuit to generate a bias voltage for the pair of transistors; and a filter network coupled between the bias circuit and the pair of transistors to filter the bias voltage. - View Dependent Claims (26, 27, 28, 29, 30, 31)
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Specification