Cold atom interferometers allow highly sensitive measurement of inertial forces such as gravity and gravity gradients, accelerations and rotations. The atoms wave function is split in different momentum states which drift apart and later recombine to produce interference fringes, whose phase is determined by the inertial forces acting on the atoms. Measurement of unknown forces is challenging due to limited dynamic range (ambiguity beyond |ϕ| = π/2) and greatly reduced sensitivity away from mid-fringe (ϕ = 0). We present new interferometer schemes for full quadrature phase detection in a single experimental run and with a single atomic ensemble, which double the dynamic range and maintain constant sensitivity for all phases. The new schemes are realized in our fountain cold atom interferometer apparatus, where we perform gravimetry measurements at the 50 ng level.