An apparatus is provided. The apparatus comprises a first bipolar junction transistor (BJT) differential pair having a first BJT and a second BJT, a second BJT differential pair having a third BJT and a fourth BJT, a first clamp having a fifth BJT and a sixth BJT, and a second clamp having a seventh BJT and an eighth BJT. The collector and base of the third BJT are respectively coupled to the collector and base of the first BJT, and the collector and base of the fourth BJT are respectively coupled to the collector and base of the second BJT. The bases of first, second, third, and fourth BJTs receive an input clock signal. The emitters of the fifth and sixth BJTs are coupled to the collectors of the first and third BJTs, while the emitters of the seventh and eight BJTs are coupled to the collectors of the second and fourth BJTs. The bases of the fifth and seventh BJT are adapted to receive a low clamping voltage, and the bases of the sixth and eighth BJTs are adapted to receive a high clamping voltage. Additionally, the first and second clamps is coupled to the collectors of the first, second, third, and fourth BJTs.