Embodiment
Please consult Fig. 1 and Fig. 2 simultaneously, high-speed comparator better embodiment of the present invention comprises a first input end Vin+, one second input Vin-, one first output end vo ut+, one second output end vo ut-, one first switch element, a second switch element, one the 3rd switch element, one first resistance R 1, one second resistance R 2, one the 3rd resistance R 3, one the 4th resistance R 4 and one the 5th resistance R 5.This first input end Vin+ and this second input Vin-are used to receive a pair of differential signal of input, and this first output end vo ut+ and this second output end vo ut-are used to receive a pair of differential signal of output.
In the present embodiment, this first switch element is one first field effect transistor M1A, and this second switch element is one second field effect transistor M1B, and the 3rd switch element is one the 3rd field effect transistor M3.This first field effect transistor M1A, this second field effect transistor M1B and the 3rd field effect transistor M3 are N type field effect transistor (NMOS).In other embodiments, switch element can change to switch element or the circuit that can realize said function as required.
The annexation of this high-speed comparator better embodiment is: the grid of this first field effect transistor M1A connects this first input end Vin+, its drain electrode connects an end of this first output end vo ut+ and this first resistance R 1, and its source class connects an end of the 3rd resistance R 3.The grid of this second field effect transistor M1B connects this second input Vin-, and its drain electrode connects an end of this second output end vo ut-and this second resistance R 2, and its source class connects an end of the 4th resistance R 4.The other end of this first resistance R 1 and the other end of this second resistance R 2 are connected an end of the 5th resistance R 5 jointly, and the other end of the 5th resistance R 5 connects a power end VDD.The other end of the 3rd resistance R 3 and the other end of the 4th resistance R 4 are connected the drain electrode of the 3rd field effect transistor M3 jointly, and the grid of the 3rd field effect transistor M3 connects a voltage end Vb, and its source class connects an earth terminal VSS.
See also Fig. 3, another execution mode of high-speed comparator of the present invention comprises first input end Vin+, the second input Vin-, the first output end vo ut+, the second output end vo ut-, one the 4th switch element, one the 5th switch element, one the 6th switch element, one the 6th resistance R 6, one the 7th resistance R 7, one the 8th resistance R 8, one the 9th resistance R 9 and 1 the tenth resistance R 10.This first input end Vin+ and this second input Vin-are used to receive a pair of differential signal of input, and this first output end vo ut+ and this second output end vo ut-are used to receive a pair of differential signal of output.
In this another execution mode, the 4th switch element is one the 4th field effect transistor M2A, and the 5th switch element is one the 5th field effect transistor M2B, and the 6th switch element is one the 6th field effect transistor M4.The 4th field effect transistor M2A, the 5th field effect transistor M2B and the 6th field effect transistor M4 are P type field effect transistor (PMOS).In other embodiments, switch element can change to switch element or the circuit that can realize said function as required.
The annexation of this another execution mode of high-speed comparator is: the grid of the 4th field effect transistor M2A connects this first input end Vin+, its source class connects an end of the 6th resistance R 3, and its drain electrode connects an end of this first output end vo ut+ and the 8th resistance R 8.The grid of the 5th field effect transistor M2B connects this second input Vin-, and its source class connects an end of the 7th resistance R 7, and its drain electrode connects an end of this second output end vo ut-and the 9th resistance R 9.The other end of the 6th resistance R 6 and the other end of the 7th resistance R 7 are connected the drain electrode of the 6th field effect transistor M4 jointly, and the grid of the 6th field effect transistor M4 connects a voltage end Vbp, and its source class connects power end VDD.The other end of the 8th resistance R 8 and the other end of the 9th resistance R 9 are connected an end of the tenth resistance R 10 jointly, and the other end of the tenth resistance R 10 connects earth terminal VSS.
Circuit with Fig. 1 is an example, and the principle Analysis of this high-speed comparator better embodiment is as follows:
1. gain is derived
In the present embodiment, suppose R1=R2=Rd, R3=R4=Rs, the first field effect transistor M1A, the second field effect transistor M1B are input pipe, and this high-speed comparator is carried out monolateral equivalence, can obtain its gain formula and be:
Vout/Vin=-gm·ro·Rd/(Rd+Rs+ro·(1+(gm+gmb)·Rs))
Wherein Vout represents output voltage, and Vin represents input voltage, and gm represents the mutual conductance of the first field effect transistor M1A, and gmb represents the mutual conductance of the second field effect transistor M1B, and ro represents the small-signal output resistance.By suitable biasing, make (gm+gmb) Rsro " Rd, Rs, ro, then gain formula can be reduced to
Vout/Vin=-Rd/ ((1+ η) Rs), wherein η=gmb/gm
Can be got by following formula, the gain of this high-speed comparator is only relevant with Rd, Rs, gmb/gm, if do not consider to serve as a contrast inclined to one side effect, i.e. and metal-oxide-semiconductor source end and substrate short circuit, then gain formula can be changed into:
Vout/Vin=-Rd/Rs
We can mate Rd, Rs in domain accurately, and then its gain is just no longer with the technology conversion, and also irrelevant with bias current.
2. bandwidth analysis
Suppose that the output limit is Pout, make that load capacitance is Cout, then
Pout=1/(Rd·Cout)
Generally speaking, Rd is 5 ~ 10kohm(kilohm), Cout multiply by 10 negative 15 powers for the 50fF(farad), Pout=2 ~ 4GHz(Gigahertz then).
3. cascade
This structure one pass gain is not high, can possess filter effect simultaneously by cascade to obtain high-gain.
High-speed comparator of the present invention is simple in structure, and gain does not change with technique change, and only relevant with the resistors match degree at leakage two ends, field effect transistor source, its bandwidth can be accomplished the GHz level by comparator output resistance and the decision of next stage load capacitance simultaneously.