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This paper reports on the design and characterization of a high-gain tunable transimpedance amplifier (TIA) suitable for gigahertz oscillators that use high-Q lateral micromechanical resonators with large motional resistance and large shunt parasitic capacitance. The TIA consists of a low-power broadband current pre-amplifler combined with a current-to-voltage conversion stage to boost the input current before delivering it to feedback voltage amplifiers. Using this approach, the TIA achieves a constant gain of 76 dB-Ohm up to 1.7 GHz when connected to a 2 pF load at the input and output with an input-referred noise below 10 pA/√(Hz) in the 100 MHz to 1 GHz range. The TIA is fabricated in a 1P6M 0.18 μm CMOS process and consumes 7.2 mW. To demonstrate its performance in high frequency lateral micromechanical oscillator applications, the TIA is wirebonded to a 724 MHz high-motional resistance (Qunloaded ≈ 2000, Rm ≈ 750 Ω, CP ≈ 2 pF) and a 1.006 GHz high-parasitic (Qunloaded ≈ 7100, Rm ≈ 150 Ω, CP ≈ 3.2 pF) AIN-on-Silicon resonator. The 724 MHz and 1.006 GHz oscillators achieve phase-noise better than -87 dBc/Hz and -94 dBc/Hz @ 1 kHz offset, respectively, with a floor around -154 dBc/Hz. The 1.006 GHz oscillator achieves the highest reported figure of merit (FoM) among lateral piezoelectric micromechanical oscillators and meets the phase-noise requirements for most 2G and 3G cellular standards including GSM 900 MHz, GSM 1800 MHz, and HSDPA.