This paper proposes the employment of trelliscoded-modulation (TCM) to improve error performance and/or to increase system throughput in a multi-gigabit physical layer (PHY) design for millimeter-wave 60GHz wireless personal area network (WPAN) systems. Hardware impairments such as the 60GHz power amplifier (PA) non-linear distortion and the 60GHz phase-locked loop (PLL) phase noise (PN) are considered in the system design. It is found that for residential environment, in the AWGN and line-of-sight (LOS) multipath channels, TCM with hard decision Viterbi decoding is able to offer coding gain of approximately 1.5dB, and in the non-line-of-sight (NLOS) multipath channel, approximately 1.2dB, compared with quadrature phase shift keying (QPSK). By considering non-linear distortion in the PA, bit error rate (BER) degradation of 0.8dB is observed in LOS channel. As for NLOS channel, the same non-linear distortion causes error floor at BER=10-5. It is also observed that a maximum of 2-times improvement of the PHY throughput can be achieved by TCM in the NLOS environment. Additional gain of 0.8dB can be obtained in NLOS channels by employing longer decoder traceback length (TBL) of 20 instead of 10.