CA3140E - High-Input-Impedance Operational Amplifier

Overview

The CA3140E is a high-performance operational amplifier that combines the advantages of MOSFET and bipolar transistor technologies. As illustrated in its block diagram, this device features an input stage capable of operating down to 0.5V below the negative supply rail. The amplifier architecture consists of two class A amplifier stages for voltage gain and a unique class AB amplifier stage for current gain, making it particularly suitable for applications requiring high input impedance and wide voltage range operation.

Key Features

MOSFET Input Stage Characteristics

• Extremely High Input Impedance: Typical value of 1.5TΩ (1.5 × 10¹² Ω)
• Ultra-Low Input Current: Just 10pA typical at ±15V supply voltages
• Wide Common-Mode Input Voltage Range: Can swing 0.5V below the negative supply voltage rail
• Complementary Output Swing: Matches the input common-mode range for maximum signal handling

General Performance Features

• Direct replacement for industry-standard 741 op-amps in most applications
• Excellent frequency response characteristics
• Low power consumption compared to bipolar-input op-amps
• Stable operation over wide temperature ranges

Applications

The CA3140E's unique combination of characteristics makes it ideal for numerous applications:

• Ground-Referenced Single Supply Amplifiers: Particularly in automotive and industrial control systems
• Sample-and-Hold Circuits: Benefiting from the extremely low input current
• High-Impedance Buffers: For instrumentation and measurement equipment
• Active Filters: Where high input impedance is critical
• Photodiode Amplifiers: Taking advantage of the low input bias current
• Medical Instrumentation: For ECG amplifiers and other sensitive measurements
• Long-Duration Timers: Due to minimal input current errors

Electrical Characteristics

(All specifications at ±15V supply voltage and room temperature unless otherwise noted)

Input Characteristics

• Input Offset Voltage: 5mV maximum
• Input Bias Current: 10pA typical, 50pA maximum
• Input Offset Current: 0.5pA typical, 10pA maximum
• Input Resistance: 1.5TΩ typical
• Common Mode Input Voltage Range: -0.5V to +12V (at ±15V supplies)
• Common Mode Rejection Ratio: 90dB typical

Output Characteristics

• Output Voltage Swing: ±13V minimum into 2kΩ load
• Output Current: 20mA minimum
• Output Resistance: 60Ω typical

Dynamic Characteristics

• Slew Rate: 9V/µs typical
• Gain Bandwidth Product: 4.5MHz typical
• Rise Time: 0.08µs typical

Power Supply Characteristics

• Supply Voltage Range: ±5V to ±15V
• Supply Current: 4mA typical
• Power Consumption: 120mW typical at ±15V

Package Information

The CA3140E is available in several industry-standard packages:

8-Pin DIP (Dual Inline Package)

• Package Code: E (for CA3140E)
• Dimensions: 9.81mm × 6.35mm body
• Pin Spacing: 2.54mm (0.1") between pins, 7.62mm (0.3") row spacing
• Lead Material: Copper alloy
• Finish: Matte tin plating

8-Pin SOIC (Small Outline Integrated Circuit)

• Package Code: M (for CA3140M)
• Dimensions: 4.9mm × 3.9mm body
• Pin Spacing: 1.27mm pitch
• Height: 1.75mm maximum

Thermal Characteristics

• Junction-to-Ambient Thermal Resistance (θJA): 100°C/W (DIP package)
• Junction-to-Case Thermal Resistance (θJC): 45°C/W (DIP package)
• Maximum Junction Temperature: 150°C
• Operating Temperature Range: -55°C to +125°C

Design Considerations

PCB Layout Recommendations

• Use proper grounding techniques to minimize noise pickup
• Keep input traces short to prevent stray capacitance
• Bypass power supply pins with 0.1µF ceramic capacitors placed close to the package
• For high-frequency applications, consider a ground plane

Stability Considerations

• The amplifier is internally compensated for unity-gain stability
• For non-inverting configurations with gain less than 10, additional compensation may be needed
• Avoid excessive capacitive loading (>100pF) directly on the output

Comparison with Industry Standards

The CA3140E offers significant advantages over traditional bipolar-input op-amps like the 741:

• Input current approximately 100,000 times lower than bipolar op-amps
• Input impedance several orders of magnitude higher
• Wider common-mode input voltage range, especially near the negative rail
• Faster slew rate (9V/µs vs 0.5V/µs for 741)
• Higher gain-bandwidth product (4.5MHz vs 1MHz for 741)

Reliability and Qualification

• Manufactured under strict quality control procedures
• ESD protection on all pins (2000V HBM minimum)
• Available in commercial, industrial, and military temperature grades
• RoHS compliant versions available