A Design Of High PSR CMOS Reference Source

Reference sources are widely used in analog and mix-mode circuits, such as A/D, D/A converters, voltage regulators, measurements, instrumentation circuits, and bias circuits. Reference source outputs a stable reference signal which is independent of power supply voltage, temperature and process. This thesis designed a current reference source which was applied in tuner chip for Digital TV. The function of the current reference source is to supply a dc stable bias current for the other circuits in the chip. The design of the current source included two parts, one was the voltage reference source which generated a stable output voltage and the other was the V-I converter circuit which converted the reference voltage to reference current and output it to the other blocks in the chip.The design of voltage reference in this thesis adapted band-gap first-order temperature compensation technique, and the simulation result of temperature coefficient (TC for short) of the output voltage is 14.6ppm/℃. This thesis analyzed five mismatch errors due to process in the band-gap voltage reference. They are current mirror mismatch, resistor mismatch, resistor tolerance, offset voltage and bipolar transistor mismatch. This thesis analyzed the influence of each mismatch error and proposed improving methods. Since the chip is applied in RF receiver system, and the operation frequency is extended to 1GHz, the power supply rejection (PSR for short) performance of the reference source in the whole frequency range will influence the whole chip performance especially in high frequency because that due to the existing of the capacitive through and the reduction in the loop gain with frequency, spurious signals coming from the power supply line cannot be adequately rejected. This thesis analyzed the PSR performance of the band-gap voltage reference through modeling the PSR performance in frequency domain and detruding the transfunction expression of PSR. This thesis also adjusted the parameter based on the transfunction expression, and used a compensation capacitor to improve the PSR performance. The simulation result of PSR performance after optimization is -103dB in low frequency and lower than -50dB in high frequency.The design of V-I convert circuit in this thesis adapted a Series-Series feedback circuit which was consisted of a NMOS and a low TC resistor. It used a high gain OPA to increase the transconductor of the NMOS to stabilize the reference current. The low TC resistor was combined of two poly resistors with different TC in series. This thesis also analyzed the parameter mismatch as offset voltage of the OPA, resistor tolerance and current mirror mismatch in the V-I convert circuits and adapted an adjustable current mirror ratio circuit to trimming the output reference current. The simulation result of TC of the output current is 48ppm/℃, and power supply stability is smaller than 0.64% (2.5V~4V).The design reference source in this thesis was fabricated in Chartered 0.25μm N-well CMOS process. All the simulation results were based on Hspice simulator, and the modeling analysis used matlab tool. The chip was fabricated in Chartered. The measurement results of the current reference source showed that the power supply stability of the output reference current is 1.7% (2.5V~4V), and the trend along the temperature of the test point is the same with simulation result which is direct proportion to temperature.