HJ8038 Precision Function Generator Full-Temperature-Range Operating Guide

In modern electronic devices, operational amplifiers are an indispensable component. Particularly in the design of domestically produced op‑amp circuits, selecting appropriate components and optimizing the circuit architecture have become focal points for many engineers. Today, we will delve into the key principles and techniques of designing domestic op‑amp circuits, helping you elevate your circuit‑design expertise. 1. Understand the Basic Characteristics of Operational Amplifiers First and foremost, when designing a domestic op‑amp circuit, it is essential to grasp the amplifier’s fundamental characteristics. The core performance of an op‑amp hinges on parameters such as gain, input impedance, and output impedance. Gain determines the signal‑amplification capability; input impedance affects the source‑load interaction; and output impedance influences the signal‑transmission efficiency. Only by thoroughly understanding these basic traits can we proceed with more effective circuit design. 2. Choose the Right Domestic Operational Amplifier While the market offers a wide array of domestically manufactured op‑amps, not every model is suitable for your specific project. When making your selection, consider several critical factors: bandwidth, power consumption, operating temperature range, and cost. For instance, if your application involves high‑frequency signal processing, bandwidth becomes the primary consideration. Conversely, for projects with stringent low‑power requirements, prioritize low‑power consumption.

Experimental Background

　　During the use of the HJ8038, the customer observed harmonic distortion in the sine wave. Upon learning of this issue, our technical team reproduced the problem and investigated potential improvement measures, based on the customer’s feedback. In addition, we conducted further testing of the device’s performance parameters under full‑temperature conditions.

　　The final experimental results are as follows:

　　1. The application circuit of HJ8038 has been optimized, as shown in Figures 1 and 2. By adding a tuning circuit, harmonic distortion has been reduced, ensuring that the harmonic distortion parameters meet the user’s requirements.

　　2. During the experiment, it was observed that variations in the system’s supply voltage directly affect the amplitude of the output waveform. Test data are presented in Table 1. It is recommended that users employ a power‑supply circuit with high precision and low temperature drift for power distribution.

　　3. The HJ8038 has relatively high self‑consumption (at +15 V supply, IDD = 20 mA, resulting in a power dissipation of P = 300 mW). Users should take thermal dissipation into account and either provide an appropriate heat sink or incorporate adequate thermal management during PCB layout.

　　4. Performance testing of the HJ8038 across the full temperature range of −55°C to +125°C (under a 15 mA load) revealed that the device operates normally and stably throughout this temperature span.

　　Product Overview

　　The HJ8038 precision function generator is a monolithic integrated circuit chip fabricated using advanced technologies such as Schottky barrier diodes. It boasts a wide supply‑voltage range, high stability, high accuracy, and ease of use, requiring only a minimal number of external components to operate. It can simultaneously generate square, triangular, and sine waves, with the frequency of its output waveforms controlled by either an internal or an external voltage. It is suitable for applications such as voltage‑controlled oscillators and FSK modulators. The device can directly replace the ICL8038, and it has now been fully domestically produced.

　　Features:

　　It can simultaneously output arbitrary triangular, square, and sine waves.

　　Frequency range: 0.001 Hz to 300 kHz

　　Duty cycle range: 2% to 98%

　　Low-distortion sine wave: 5%

　　Low temperature drift: 50 ppm/°C

　　Sine wave output linearity: 0.1%

　　Operating power supply: ±7 V to ±14 V or +14 V to +28 V

Electrical Principle Block Diagram

Package and Lead Terminal Functions

     It employs the purple ceramic flat 14‑lead package (F14‑01) and the purple ceramic dual‑in-line 14‑lead package (D14S2).

The arrangement and functions of the lead terminals are shown in Figure 8.

Absolute Maximum Ratings

  Electrical characteristics

Unless otherwise specified, T _A =25℃, VS=±10V or +20V, R _L =10 kΩ.

Actual product image

Typical Applications

1. The output frequency of the signal generator is f = 0.33 / (R·C), where R = R _A =R _B ), it is recommended to use resistors and capacitors with high stability and high precision;

2. If waveform distortion occurs, the waveform can be adjusted by varying the resistance values of the sliding rheostats RT1 and RT4.

3. If the V+ and V− errors/noise are significant, to ensure output stability, it is recommended to power the circuit using a reference voltage source.