We present a microwave frequency standard based on coherent population trapping (CPT) in the ${}^{87}\mathrm{Rb}{D}_1$ line. The CPT spectrum is obtained using two Raman lasers with a $6.8\mathrm{GHz}$ frequency offset by injection locking of a master laser to a slave laser. We have constructed an atomic clock employing a $5\mathrm{cm}$ long Rb vapor cell confined with $6.67\mathrm{kPa}$ neon buffer gas at $70°\mathrm{C}$ . Using this system, we improve the CPT contrast through the elimination of undesired off-resonant fields created by the direct modulation method. We measured the frequency shift of the CPT signal as a function of the temperature of the Rb cell and estimated it to be approximately $1.3\times {10}^{-9}∕\mathrm{K}$ . The frequency of a $10\mathrm{MHz}$ crystal oscillator has been stabilized to the CPT spectrum between the two ground states in ${}^{87}\mathrm{Rb}$ . The relative frequency stability is approximately $2.3\times {10}^{-12}$ for an average time of $68\mathrm{s}$ .