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  1. #1
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    Design of a Comparator

    please suggest a circuit to design a comparator with the following specifications



    Process 180nm CMOS

    Power Supply 1.8V

    CLK to Output Delay <11ns

    Input Voltage range 600 to 1200mV

    Differential Swing 1.2V

    Power consumption <2mW

    Estimated Load Capacitance 100fF



    thanks in advance

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  2. #2
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    Re: Design of a Comparator

    taking into account low gain requirement (i.e. "differential swing 1.2V") you need a complementary (P-type+N-type, to cover 0.6...1.2V input range) low gain (e.g. 2...4...8, to be fast) differential stage followed by simple regenerative amplifier. Might be enebled RS-latch as last stage shall be added, if comparison state have to keeped during whole clock cycle.


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  3. #3
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    Re: Design of a Comparator

    Please can u tell me what does a low gain differential stage mean?



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    Re: Design of a Comparator

    this means differential amplifier with ratio between driver to load transconductance (Gm/Gload) <10. In principle from your spec follow that even simple complementary (i.e. P-type + N-type sensitive input) regenerative amplifier (without analog preamplifier stage) can be enough.



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    Re: Design of a Comparator

    can u please explain me a little more about ur recent post i.e.,simple complementary (i.e. P-type + N-type sensitive input) regenerative amplifier (without analog preamplifier stage)
    I am actually new to analog designing



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    Re: Design of a Comparator

    input voltage sensing transistors could be N-type or P-type or both P+N-type (i.e. complementary) pair (quad) of transistors. Last case expand allowable range of common mode input voltages. Example of such simple comparator you can find on figure
    http://images.elektroda.net/50_1308299921.jpg



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    Re: Design of a Comparator

    Can you please give me some material related to the circuit?

    Or is there any possibility to make a comparator working for 10mV input to work at my required voltage range?



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  8. #8
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    Re: Design of a Comparator

    There are a lot of materials related to analog circuit design. You themself should to define a region of interests and use Google. As a beginner you can start from any classic, say "CMOS Analog Circuit Design" of Allen, Holberg.
    Rgarding 10mV sensitivity level for your comparator it can be repeated that low gain preamplifier should be used before regenerative comparator in that case. Because regenerative comparators have usually good sensitivity (~5mV), but they typically have big input offset voltage.


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